I went thru this a couple years ago.

First, many of the 'R12' replacements are based on propane. Some might wonder about the safety issues of a highly flammable refrigerant.

Second, yes, R12 is available but there are also many selling recovered Rxxx and calling it R12 to make a little extra money.

Third, getting the R12 is the easy part. Most A/C shops have discarded the equipment (gauges, recovery tank, etc.) since there's no business for it any more. So finding someone competent to do R12 is getting harder.

In the end I decided the best thing was to replace the hoses, drier, etc., flush the system and replace with R134 and the proper oil. It didn't seem to get as cold (it shouldn't) but it got cold enough.

Good luck.