If you don't have an A/C license, you can't even get R12 here. Even then, it's in something like a 25 lb can. An HVAC supply house would be the best source.
There's a low pressure switch on the A/C system that is supposed to shut down the compressor under low freon conditions. The suggestion to run a lead to the compressor clutch with the motor running to test the clutch and compressor is a good one.
There are some A/C techs on FABO. Hopefully one will chime in with some skilled direction to resolving the problem.
