I think it was either Jo-Han or MPC that tooled up the 1971 Superbird. They got the drawings from Mpar when they were actually styling up the 1971 Superbird. There were a few clay mockups for wind tunnel testing, but as we know the program was scrapped.
And yes, every once in a while the kit of the 1971 Superbird shows up on eBay. The last one I remember that was unbuilt went for something in the neighborhood of $286 or so.