if someone wants to shake the tree and find lost, rare chips you have to put some bait out there. The fact you never see these trade in the classifieds tells you the owners aren't lined up to sell. They have to be seduced. So shocked by the offer that the current collectors reconsider.
You willing to pay Big Bucks/per chip? Say so. If all you have is "chump change" you aren't buying anything, much less a full rack.
Good luck. Expect to pay through the nose -=- DrStrange