Most likely it is celluloid. You can still get celluloid from a number suppliers in the US but the prices have become elevated, and suppliers fewer, because the shipping companies have labeled raw celluloid as a hazardous material so you have to pay a flat fee to ship it regardless of how much you ship. There are a few companies who don't charge that fee. Of course, it doesn't make much sense because those fees aren't attached to products that have celluloid on them. Most side dots are ABS plastic.