R12 is really easy to find, just transfering it from unit to another take a bit of messing around with adapters and hoses. you just have to look for old fridges and transfer it over, ive done it on a few friends vehicles before. like i said it is difficult but doable, if not any auto place make a R!@ substitute you can get in the small cans that are recharge kits they also work well even in the old R12 setups
DCC, good to hear that the GTD AC works well on R134. Was a bigger or more efficient condenser put in?