In the UK at least, there are a number of on line dealers for classical LPs, not CDs. They will buy large numbers. Inevitably, if you let them choose what they want, you'll get more than if you insist they take everything.
Classical LP & CD Collection - How do You Sell When Record Stores Don't Want?
I have 250+ classical LPs many in M- condition for the vinyl and 300+ classical CDs that I want to start selling off. I recently brought a box of them to a record store and the owner just said "I can't sell this stuff!". Do you have any suggestions? I was thinking of offering in specific groupings all the Argo, Deutsche Grammophon, RCA etc. etc. I'm not trying to make top dollar on anything just the collection has gotten large and something has to go.