R12 was the default refrigerant for all automotive AC systems through about 1993 or 94.
There are refrigerant blends out there that have similar properties for restoration purposes. There are also retrofit kits out there for 134A. Just remember that the two never mix - R12 uses a different oil than R134a. So your entire system will need to be thoroughly cleaned out, and you will require a new dryer.
I had a retrofit to 134a done to my 68 Cadillac to cosmetically look like OEM. It was performed by Classic Auto Air in Tampa several years ago. The project cost $2500 and it uses all of the OE or very close to OE components under the hood. If authenticity is not what you are after, it may cost slightly less.
