Gees i bet the government wants to know who is still selling R12 a/c refrigerant. as it was phased out in 1996, and is pretty much illeagal to use/sell in this and just about every country in the world.
there was a gas made up when they phased R12 out, but it was only used for a few years as a substitute untill R134a was standard.
R12 is an ozone depleting gas. So if you want this planet to be around for your future generations i would suggest doing the right thing and convert the system to R134a
+ i would report whoever told you they could get you R12 becuase they are dodgy and i wouldn't trust them with my car anyway!