Hiya Nancy, I agree that these 5 & 100 chips are available, at least in the small key series. The 25 may require some extra hunting. The guide values seem to reflect a premium that a very early, attractive Las Vegas strip property chip would have. I got my examples on eBay at what I would term a wholesale price
Seems eBay is the place to make low book bids with success. Yes, the numbers are the chip denomination, a convention sometimes seen on '40's chips.
There is also a series of chips with the same covered wagon image, crest & seals, that are probably genuinely rare and very pricey if'n you could find any, I imagine.
I've seen a postcard with the wagon on it, an attraction at this western themed resort, I recall that it said "Vegas or Bust" on the side. When Bugsy and Billy Wilkerson were building The Flamingo, they stayed at the Last Frontier so maybe they wagered these very chips! Or maybe not.