Sound like MastaHanky discovered Patelson's Music, just across the street from the stage door entrance to Carnegie Hall. I drop in there every other month or so to check out the sale books at the front of the store and to browse through the used sheet music in the back. There used to be a store called Gryphon on the UWS which sold lots of all sorts of classical vinyl records, books and scores, and perhaps CDs as well. I believe they are still in business, but I am not sure exactly where now. (They used to be just west of HMV records on 72nd street...