I have a catera with a broken fuel door, is there a company that sells a billet type replacement?

Not that we are aware of....

its easy fix, my hinge broke too and i drilled a small hole through the base and the fuel door hinge and inserted a small bolt with a nut there, it works like a charm...
So i dont know how bad yours broke but if the piece is not too shatered its fixable. otherwise check the junk yards for a different door.