Your best bet is with the CMP. If you're near the base at Camp Perry Ohio, you can go there and check them out for yourself, and buy one if you qualify.
Just an FYI, all the M1s from the US government have been rearsenaled several times, and are very likely mismatched with parts from different eras. They are perfectly functional and wonderful to shoot, but if you want an authentic 1940s Garand, with the proper parts on it, expect to pay upwards of $1500 for one, if you're luck enough to find one that has been restored properly (which by the way, means you better know what you are looking at to avoid buying a faked rifle).
The M1s served WWII, Korea and then were given to foreign nations and the US national guard when the M14s came to replace them. If you remember the massacre at Kent State Univ. in the early 70s, the national guard did their shooting with the M1s. A few years later they were officially retired from service here in the US, and made available to buy via the CMP. On a last thought - I noticed that in the movie "JAWS", the guy was using an M1 to shoot the big shark.