Where do you buy your CDs these days?


I'm curious what online sites folks use to find CDs? I use Amazon, and especially their Marketplace sellers for used discs. But prices have become high and supply has become stagnant. I used to use several European retailers (Amazon UK and Presto) before the pandemic, but shipping is extremely slow these days and I've had more than one never show up at all and presumed lost. Surely there are other online retailers?
drowe
You can't beat Half Priced Books and occasionally Goodwill but since I've added Pandora and Spotify, I rarely buy CD's anymore and have tons I don't even listen to. 
Usually eBay for CD's, if you know a prime member Amazon can be okay. Lp's from eBay, Pop Market and Discogs I've had a few problems with lp condition lately but usually everything is fine.Pop Market has some interesting finds in the closeout section if your willing to look and now free postage. Pre pandemic I enjoyed going to new and used stores to rummage the bins.
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Besides Amazon and eBay, I would try Berkshire Record Outlet, broinc.com
Heavily classical, mostly remaindered or discontinued titles at good prices. CDs and some SACDs, DVDs and Blu-Rays. They also have some jazz and world music. I usually find enough of interest to buy a batch 1 or 2 times a year.
Not sure that anyone has mentioned this, but Deep Discount is also a good alternative for both music and movies.  
Amazon & Smithsonian. Used on eBay. Used Oldies in the past but service and quality can be sketchy so no more. Locally Goodwill and a few reseller's work if you can examine the product before buying.
Nice not to be tied to your ISP or streaming service for your music.
Then there is always NPR - if you still have a tuner.
+1 Discogs.  I also use dr-wars.com First for checking the quality of the recordings before I buy anything,  very helpful.  and I then I can use Amazon Prime if cost is competitive. I’ve found some “jewels “ from them. And eBay too...
Cheers
I buy new classical CD's and SACD's from PrestoClassical in the UK.  However, their shipping prices have just increased a lot, so Amazon Prime may become my source.
Epilog: Today most CDs are mastered way to LOUD. You can find the problem described if you search for LOUDNESSWAR on youtube.
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Because of the LOUDNESSWAR, I do not buy new CDs ever.
LPs can NOT be LOUDNESSWAR mastered, so new albums sound way better on LP.
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DISCOCGS is always my go-to-site for CDs or LPs in physical form.
It is superb sorted and I can search for CDs with proper mastering printed before 1990.
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The proper thing to do than, would be to rip them with EAC (Exact Audio Copy) on a PC which makes sure by comparing the signatures with its database that everything is ripped bitperfect.
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After that I convert the FLAC to iTunes lossless ADAC with XLD.
.. to feed my non-oversampling DAC (Metrum Amethyst) and tube amp.
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best regards form Austria (Europe, not the kangaroos)
@jbmays   Don't know about your library, but my library discontinued CD's three years ago.  All you can get now is downloads, and I think they are MP3's. 
I still buy CD's and enjoy their sound and convenience.  All of my purchases are through Amazon these days.  It is the best place to find obscure albums.  Vinyl, CD's, streaming, it's all good played through quality equipment.
Not sure where you are, but I live in Tampa. There's an outlet here called Sound Exchange that has thousands of new and used CD's. They never used to ship, but now with the pandemic, they were shipping. Not sure if they will continue, but you can check with them. You can Google them and get their contact info.
To add:
You can usually preview the tracks on Discogs. If not, there is always youtube to preview first.
Hi,
I buy used, mint or near mint condition CD's, from Discogs site.
I will go to Steve Hoffmans site online, to research opinions  on a particular CD I may be interested in buying. There is almost always a consensus, within the many posts, of what particular "pressing" ,of a certain CD, is the best sounding, and which suck: AM+ Japanese mini lp style, MOFI, etc., to name just a few.
You can then enter your choice into Discogs search bar, and find hundreds of sellers of the CD you want. It will list various prices, locations, and condition.
I click on $USD. mint or near mint, and I get a list, at various prices, and geographical locations of the seller, to choose from.
Very reasonable prices, and sellers have feedback listed by their name.
Very happy with the results. I have bought several hundred CD's, over the years.
Here's a no-brainer:   go to your local public library, check out 20 CDs at a time;  preview in your car while driving over the next week or two.  Rip the ones you like at home, return all---FREE!!
A year or two ago I scored 155 CDs (a great mixture of jazz, blues and classical) on eBay for $65 + $27 s/h.  Among other great discs, the lot included Frank Morgan's "Mood Indigo" (ono the Island label) which, besides being a great collection of music, is worth about $20 on it's own. Great bargains to be had if you're willing to just..............shop.   
eBay, Discogs, Bandcamp, used from local brick and mortar shops (pre-COVID), and order direct from record labels. 
Amazon, ebay, Music Direct,  and Acoustic sounds. I just bought one from Acoustic Sounds for .99 plus shipping ( 4.17 ). Vinny Valentino / Now and Again. 
Post removed 
If your getting 1.99 plus shipping...your getting top dollar.You don't  even have cases .I buy ebay,but want a case .
I have a few CD's I am throwing away. I got my old CD's and SACD's out of storage and set them up on my CD rack. However, the extras that did not fit on the rack are going to be removed. I see that Goodwill may take these CD from the posts on this thread.

I have a bunch of Stereophile audiophile recordings from maybe 15 years ago. I never listened to them much but someone on Audiogon may like them. They are free to anyone who wants to pay for the shipping.
Second Amazon/eBay, but I only buy new or pristine CD's nowadays because my Cambridge Audio CXC transport hiccups at the very hint of a scratch or scuff, whereas my Oppo BDP-103 would play with nearly a complaint (AND it played SACD's, too!). 
I buy all used CDs on eBay. It usually ends up being from declutter. Low prices, low or no shipping, fast delivery. I research via the DR database first to at least rule out the bad/compressed recordings. Most 'remastered' CDs are worse than the originals, sometimes waaaaaaaay worse.

I buy new CDs, usually only new artists, from Amazon. They almost universally cost too much and are almost universally DR compressed. I know this going in and a lot of what drives buying it is to support a new band. Not sure how much they get per CD. Maybe nothing.

I just got a SACD player. Not sure I'm going to go down that path unless it is something really special.
You have already got a lot of recommendations about buying cd:s. If you want to buy downloads you can try HD Tracks.

You will still "own" the music you have bought and it should work as long as there are equipment to play it on and that will probably be longer than there are cd players. You do need a player/streamer with storage or a network attached storage (NAS) that your streamer can get the music from.

https://www.hdtracks.com/
https://www.amoeba.com/music/cd-and-vinyl/#/
I try not to give money to Amazon. 

I second the recommendation for discogs, too, though the site design is not awesome.

I bought a bunch directly from the great Americana label New West last time they had a five dollar sale. Richard Thompson, John Hiatt, and Rodney Crowell albums for five bucks!
Deepdiscount.com has some great deals and coupons sometimes.  I use them and have always been happy.
I used to buy almost all my CDs from Second Spin. But alas, another casualty of our times. Ebay seems to be the best alternative along with Amazon. 
+1 audioguy85 & others who have named thrift stores like Goodwill. I found a thrift store in Richmond Va that has an incredible selection of classical CD's. I've probably bought close to 100 from that 1 store. Also, a lot of people have mentioned eBay and that is a great source of almost any CD you could be looking for. I just bought a 20 CD set of Artur Rubinstein playing Chopin for $25. That's a deal. It's from old recordings and originally recorded in mono (which actually makes sense to me when you're recording a solo instrument) and it sounds superb when you turn it up a little. 
The great thing about the thrift stores or Goodwill is that you get some rare items that are out of print, or cost $40-$80 if you can get them new. You have to sift through a lot of junk to find the jewels but it's fun!
Well today ended the drought at one of my local charity shops, bunch of new stock in the CD section, found 6 to bring home.
And it was 50% of for VIP members so just $1 each.
Ripping to hard drive right now via JRiver........
I buy quite a few CDs these days because they are so cheap. I usually buy used.

decluttr.com, Amazon and eBay are where I get most of them.
I try to buy directly from the artist at a show. But no shows now. Also, many artists have their own site or their label will sell direct.
For example:  http://www.signaturesounds.com
     https://www.paradiddlerecords.com

There's a used record store, not close, where I picked-up a handful, and LPs as well for cheap. 

Amazon for usual R&R, but rarely.

What's Streaming?  : )  Guess that's where it's going.

Got son a disc of Marches for Christmas. He looked at it with a small bit of distain, saying he can get it on (some streaming service) I said, No way... He found it in two seconds, same disc!