74 Hang Ten Plastic Panel Problem

I've had my Hang Ten since 1979 and still love it after 500,000 miles! But the plastic has decided to crumble away leaving gaping holes inside. I've found replacements for everything except the panels that go around the rear tires inside. Does anyone know of a supplier for these or have any in good shape? Mine are white of course, but I'll paint any good replacement I can get.
I'm also redoing the upholstery for the second time. Any leads to a good source for the Hang Ten crazy seat fabric is welcome. Can't believe what prices I'm seeing this time around.

Thanks, JIM