In western Canada at least, there are several outlets of a place called "
Industrial Plastics & Paints" that sells everything UHMW, Teflon, or otherwise hard-to-source in plastics, in every form from tapes to huge blocks. Ostensibly a wholesaler, they still sell to the general public in some locations.
Look for such an oufit in your own neck-o'-the-woods, or consider mail-ordering. i've used them before, and they provide generally great service, and usually end up being cheaper than buying specialty pre-packaged materials from chandleries.