R12 can still be found. Its just that no one wants to be bothered playing with it. Converting everything over to R134 is often more expensive that tracking down R12. New seals (green orings) can be used for either one. R12 hoses do not have the barrier material to totally contain the R134. The old hoses can be rebuilt. The oil in the system is different between R12 and R134 so flushing is required.
To be legal, you can get a CFC certificate online. You don't need a certificate to repair the system but primarily to handle the Freon. Its pretty simple to repair the system. A vacuum pump may be the hardest tool to locate, used to evacuate and leak check. Even a gauge set is not that pricey. If you have R12 freon in your system now, it may just be low. Look for greasy/oily residue at the various fittings as that's a sure since of a leak. I'm not an expert but I repair my own systems. In my line of work, we used similar hardware without the CFC issue.
Just be careful of some of the substitutes, as they often contain propane. R134 does require a certificate if you purchase it in small canisters <30 lbs.
My guess, any shop is going to require you to rip everything out and start over. At that point R134 is a simple requirement.
