You can go to walmart, and buy a new replacement R-12, just put it in, it is compatable with the old freon, so no need to vacum down system, and no nbeed to change anything.
Also, i used to work for Mcmullen oil, out of clearwater, FL. they sell what they call chillit, it is also a drop in replacement.
You will not get the old stuff, and if you could, why? The new stuff, is safer for environment, and works better.