USPC c&s have 2 important things going for them with respect to rarity.

First they are much older than casino chips (made only up to mid 1940s)
Second, for the most part, relatively few were issued (maybe 100 to 200 of a particular chip). Most 300 to 500 chip racks only had 100 of each color.

I would say I have the better part of 150 one of a kinds. C&s just don't show up often.

Now, an exception is a large gambling joint that used c&s. For example I have approximately 700 JSB (Arrowhead Inn) c&s. I'm looking for more in quantity.

Here are some that I would absolurtely consider RARE (to my knowledge, may all be one of a kinds).