looking for a "plasticloth" source

I am on the search for a product I only know as plasticloth.
It us widely used to make the triangle flags used in streamers. I can find the streamers already made up with the triangle flags attached and also blank triangles but I need different sizes than the ones offered. The company I bought the blank triangle flags from does not sell the fabric.

Does anybody know of a source for a plastic coated, brightly colored fabric that heat transfer vinyl can be applied to?