My preference is always to find a really clean factory fender used. Repro fenders dont fit well and are much thinner steel. You shouldnt have trouble finding a good used 68-71 rear fender in Norcal.
Try
TheSamba.com :: Volkswagen Classifieds, photos, shows, forums, and information
you can also call CB Performance. Rick Tomlinson, the owner has a stash of used and NOS parts and may have something that he would let go.