Hey Bill;
The last time I bought any, it was the widow of the guy that had Windancer kits, that was selling off his stuff and had tons of fillet material in several sizes. Ty Marcucci posted a place either on this forum, or Stuka where he gets his from, a tool and die maker supply place. They still use it for setting up sand cast molds and stuff maybe just search leather fillets on here and on Stuka will turn up the info, and i don't think it was that long ago that Ty posted the supplier that he uses.
MERRY CHRISTMAS and HAPPY NEW YEAR!
Dan McEntee