Get your MVAC 609 certification. It's only $19.95 and an open book on-line test at
IMACA. This will entitle you to purchase any number of alternative refrigerants. Some that will work in R-12 systems are Frigc, Freezone and Freeze-12. Check out
Aircondition.com website for all the info you need to retrofit to R-134a or any of the alternatives.
mark for referral. I took a year of air conditioning and refregeration school 20 years ago but never got a freon certification required since then.