Porto Rico is only shown on the Casino Espanol card which is, undoubtedly, a PR chip. There is always the posibility of misspelling. USPC was notorious for misspellings. Porto Rico may simply be a phonetic misspelling of Puerto Rico. Heck, the spelling of Gonzalez was massacred into Gonales on the CPR card. I wouldn't pay too much attention to USPC spellings.

I realize that "casino" does not always represent a gambling joint. However, even if not a gambling joint, there would still be a great chance of the place having chips. In the same manner that the Chicago Racquet Club, Lake Shore CC, Missouri AC, Kansas City AC, etc, had chips. Many large, upper class joints had chips. Remember c&s were, as Allan Myers stated, the cadillac of gaming chips. A large place like the Casino de Puerto Rico would probably have chips available whether a gambling casino or not. I also believe that the opening date and the date of delivery of the chips is quite significant. Many of my c&c were delivered in the year that the place opened.

In any event, the chips are PR. In all probability - Casino de Puerto Rico.