Has this been discussed here before? I don't see any threads on this. Years ago I used to buy CDs from an online vendor that would send you coupons you could accumulate for future freebies. I don't even remember their name, but they had a huge selection, including vinyl as well.
About the same sources than classical.
For hires downloads: qobuz
I bought about everything edited by soundliaison (ultra hires).
For CD dodax: cheap, large choice, some OOP. Also momox.
Amazon (with their marketplace, lots OOP).
Rakuten, cheap, limited choice. Very rarely ebay.
I also bought a few jazz DVD and blurays on clicmusique (france). Cheap, but limited choice.