Watch for estate auctions and see if they don't list things like radio equipment etc.
Check club web pages in your area once in a while they have auctions.
Try Eham... oh wait...
There is not app that is going to go out and find "Ham Auctions" even if it did it would probably end up with a lot of honey smoked spiral cut hams
But its like fishing in a bad spot the bites are few and far between. You are going to have to do the legwork... sorry.