You cannot legally purchase new R12. Any R12 you find is reclaimed and thus very expensive.
Instead of recharging with R12, you'll need to have the system converted to use a compatible refrigerant like R134a. This requires not only a refrigerant change but also potentially new seals, oil, and possibly other components depending on the condition of the system. Improperly converting to R134a can damage the system. This is a job best left to a qualified automotive air conditioning technician.
