all NAPA stores stock R12 in cans. you need the cert 408 I believe, but it is easy to get online... open book test. for like 15.00
the cans are pricey, at like 25.00 each retail, if you run a shop you should not be getting cans, you should be getting drums... around $500 new.
and getting a sealed cylinder of 12 from craigslist is even cheaper... I've gotten them for free, to $100 or so for 30 POUNDS of 12...

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!