Scaling aside, if the tooling or mold isn't 100% necessary with 3D printing or even creating a CAD and burning a new mold, however, the question to me is whether BMW or Hella, regardless of any deal between them, still actually retains any rights to the design after 50 years. I'm not an IP expert but I thought design patents in the US ended after 14 years or something like that. You might not be able to sell it with the "Hella" or roundel, which are trademarked, but I'll try to figure out who can do what (or, more precisely, ask someone else to tell me).
I think John's right, though, and there just hasn't been enough of a market to induce anyone to restart production on any scale. If someone can make the different parts in small lots using essentially the same equipment and change the economics for small runs, I'm guessing BMW will gladly accept the free royalty cash on that and be happy to take credit for it to the old car owners.