I remember a place, that had replacement door tags for the later trucks that had the VIN on the dash. I don't recall a place for the Early door VIN tags. Since it will come up, I bet there is legal issues on replacing a lost VIN tag. <Many states have procedures that allow swapping VIN tags when restoring, or repairing (Generally only in cases where the dash needs replacing) VIN tags. But lost, or buying a vehicle that does not have one, gets into a very grey area.
I think you need to look into your states laws for lost VIN tags. Especially if the VIN tag shows up somewhere else. Which may easily happen, with many states requiring scrap & junkyards, to list the VIN of every vehicle they have, or passes through their facility.