134a isn't much cop for running classics, as you point out, it's expensive and comes out of the tin at too low a pressure.
You should still be able to get Sun Project "green gas" in Japan which is actually CO2 in 76g cannisters. The regs come up occasionally in shops and auctions and just clip onto your belt. They really are a spring/summer thing though, as the cooldown can be horrific. First used stock it, as did a lot of hobby shops.
You can still get the old sherman M4 HP air tanks, too, but they're bulky. The advantage there is that you can fill them off a 12v compressor running
