I had never seen them before and someone listed one on ebay for a (buy it now)... I jumped on it. It was a lower denomination chip.
Then the same guy listed the next denomination higher... adding $50 or so to the price. This went on till I started to give up not knowing how many
the guy had, but he raised the price for each new higher denomination that was listed. There were a couple of chips that others bought that same day but I've never seen them offered again.

I think there is a thread about them in the archives here... I remember making screenshots of the auctions...