Well, The Keystone Record Collector’s Pennsylvania Music Expo claims to be "the largest monthly show of its kind." I don’t know about that, but there IS a lot of stuff there. Typical stuff, LPs, CDs, 45s, even DVDs. Mostly the typical genres, old Rock, old Pop, but at least some of almost anything else, least of all classical. Their website has quite a bit of useful info if you look around, especially their "Unwanted Records" page.
recordcollectors.org/records2015/index.php
recordcollectors.org/records2015/index.php