Probably thrift stores and pawn shops. I got a Superadio II for $7 at
"Cash Convertors," a sort of second hand store but they don't do loans like
a pawn shop, and also a TRC-434 CB base station, which I bought for $30
Canadian and which went for $47 US (about $25 profit in Canadian $$). If
you were willing to pay an employee at such stores a % for leads, you could
probably make a buiness out of it.