R12 can be bought at NAPA for $30 or so a can. You can get on eBay or Craigslist even cheaper. Last year through Craigslist I bought a case of about 15 cans (12 oz.) from an 80-year old gentleman who had been saving them for his 2 antique cars. I think I gave him $180 for the whole box, which comes out to about $12 per can. Last I checked, AutoZoo was selling R134a for $10 per can. Of course you need the 609 certification to legally buy R12.

I wouldn't go with Duracool when R12 can be had cheap. Do a search here for alternative refrigerants (be careful - the threads get very heated). You will find that your system was designed for R12, so that's the best refrigerant to use in it.

The components you bought should state what refrigerants they are compatible with.

__________________
08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280