The seat belts from my 69 Dart are faded from black to greyish blue. Buckles are rusted and the retractors don't work. Is there a company that does restoration of seatbelts?
If you're not hung up on exact replacements check out Wesco Performance, they offer a lot of different lap and shoulder belts. I retrofitted my car with their retractable ones.
It would cost ~ $700 at snakeoyl. double repops. the only thing missing is the tags. I could always just save mine and sew them on....but actually? I could care less about the tags.