Some people want boxes they don't have,
some people have boxes they don't want.
Why not bring the two together? List what you have in Buy/Sell and see if you get any takers for at least some of them. I imagine somebody out there will take at least some of them off your hands . Eventually.
(Personally, I'm looking for a RailKing box that'll fit this caboose, and a MTH Premier box for a 50' boxcar)