It might be someone is making "knock offs". I can see where certain plastics would work because Poly, and Epoxy resins are both plastic.
I just can't see a non reinforced reed lasting too long without either warping or fracturing.
When I was maybe 15-16 I broke a reed in a Yamaha 175 enduro. Maybe 40 miles from home on the power line trails.
I made a replacement out of my library card, It got me home... Barely but it did work.