If I were you I would convert to R-134 if you plan to keep the car for any length of time. Reclaimed R-12 Freon is not only scarce now, it costs an arm and a leg if you do find some. I switched an old car over to the new refrigerant a few years ago. I had to replace a bad compressor anyway, so it seemed like a good time to switch over. The total cost including a rebuilt compressor and labor was around $400, and it worked great as long as I had the car.
There is a conversion kit you can buy at Walmart for about $35 that claims to convert an old system from Freon to R-134 by just changing some fittings and refilling the system with the new stuff. I have no idea how well it works, if it works at all. Of course if you live near the Mexican border you might try what #2 suggested. When I lived in FL a few years ago there was some bootleg R-12 coming into there from somewhere in the Carribean, but I heard that some of it was contaminated and would ruin your AC system. Mexican Freon might be OK though, I don't know anything about it.
That kit at Walmart is a good buy, but it leaves one major problem: The R-12 must be totally evacuated from the system
and disposed of by a professional to be "legal". Hmmm...
I wonder if my neighbor could tell if I just let it out?