Where to start? Apply the same as CDs.
Classical music? Gosh. Sooo much to choose. Genre. Composers, Orchestras, Conductors, solo artist, style,,,,,, Movies! Honestly, I don't like ALL of Bach, Mozart, Beethoven... scores. I have favorites amongst them. Older record labels. EMI. Dusch Gramaphone. Older Living Stereo. RCA ??? red label?
Search Classical Music Classics on the web. Get familiar with some names.
Stream or Youtube those selections to see if they are to your liking.
Listen to classicals on National Public Radio.
Search record labels like Mobile Fidelity, Sheffield, Telarc.. They probably cherry pick their selection due to their investment into remastering, recoding techniques...
Look for Compilations. One disk with different composers or selections. Best Of _______.
Where? Thrift stores. garage sales, auctions. Here, Agon!!! Visually inspect them if you can.
Sit while doing auction searches. Lessen the chance of injuring yourself when you fall by the prices.