They will come up from time to time. It took me a couple years to get that amount (lots of buying and cherry picking the best ones). Perfect color match to the old school Bally's (which are also a PITA to find mint).
It's a Vegas house mold set that I put together (except for the Riviera 50c chips, but I had to have those) ...the newer Flamingo's are THC mold so they won't work. There are a couple of people on PCF that sell these from time to time so hopefully you will get a bunch.