1st place to check is YourMusic.com. This is a montly club membership for CDs and SACDs at 6.99 ea. including shipping. You can join and quit at any time. One CD minimum per month. They have a minimalist collection of SACDs, but at the price, it is a good source depending on the type of music you like.
Anoher great source is Amazon.com where you can find both current and out of print SACDs, both new and used. Many of the used ones are in excellent condition. Prices can be pretty good, but the hard to get stuff is still expensive. Go to Amazon and just do a music search "SACD".
Amazon provides user reviews of the recording and performance. Yourmusic.com allows you to generally listen to portions of the songs.