I get mine usually at flea markets or second hand music shops in the next town over as I really love 80s rock and metal but you also get a ton of newish stuff.

Whenever I’m at a big electronics store like MediaMarkt in Germany they also still have CDs.

I also used sides like rebuy before, mainly for books and movies but I didn’t had a bad experience with that before.

Sometimes the bands themselves sell CDs on their fanshop.