I found the matching chip. Fortunately, it started with a "C", as I was checking alphabetically.

The Frontier chip appears to be an altered chip. The genuine red with 3-gray incused diecard chip is the $5 Castaways chip in the picture.

(However, it seems a lot of work to buy a $5 face value chip, switch the coins and sell it. I don't think I paid over $10 for the altered chip. Oh well, now I have an example of an altered chip for my collection.)

Just curious, anyone else seen metal coin switching on other chips like this?