Old stock cans of R12 are out there, but R12 is very expensive and you can't buy it without being EPA certified. I got my certification, but haven't used it in many years because at this point it doesn't make much sense. Even if you can get your hands on the R12, it is so darn expensive that it would be unwise to use it without going through the whole system first to see what is wrong.
Your best bet at this point if AC is not a familiar system to you is to get to an AC shop. If the system still has R12 in it, they'll collect it. It's a very quick process to hook up the system and see if it holds a vacuum. If not, then the leaks have to be found. Still have to diagnose the system, replace any needed things (including the 30 year old hoses and o-rings) flush out the system, and recharge with R134 and suitable new oil.