It never hurts to ask the casino for some Roulette chips; explaining that you're a collector.

Also keep in mind that there are not that many Roulette chips ordered by a casino to outfit a table as there are cash chips and a casino might not be willing to cooperate when you ask...

...but by asking you just might be surprised with what the casino would be willing to share with you; adding to your collection.

The one thing you might want to do in any casino is to tell everyone (employees) who crosses your path that you're a chip collector. Believe me... you'll be glad that you did.