Actually it's pretty rare for Boyce or some of the bigger truck (deuce and a half on up) dealers to have them anymore.
They pop up here actually from time to time and also over on
www.SteelSoldiers.com . That's a military vehicle site and it has a good CUCV forum. They show up there relatively often in the classifieds.
If you ask around there someone usually knows of one or can point you towards dealers with them.
www.idahomotorpool.com has them show up from time to time and they have a good reputation for honesty and selling good stuff.
Definitely do a search on craigslist.
www.Craigshelper.com is great for this purpose. Just do a search of your area for CUCV, M1008, M1028, Chevy military truck, etc etc etc.
They're frequently on eBay too. Use the same search terms I mentioned above.
Now to buy one directly from the government you have to go through GovernmentLiquidations or GovernmentSurplusAuctions. GL is a bit spotty and can be hard to deal with. They're also famous for mishandling vehicles and missing parts along with inaccurate descriptions. That said some people have gotten drivable vehicles from them. Most of their vehicles come straight from the military but keep in mind that these things are 20+ years old now and the military is mainly holding onto the good ones. So the stuff coming out either is seriously screwed up, the cost to fix whatever is wrong was higher/more complicated than the military thought it was worth, or the unit got entirely new vehicles and all their vehicles were surplus to requirements. However like I said some guys get trucks that just need the fluids changed and new keys. I know a guy that put new batteries in his and drove it home.
GSA mainly deals with stuff that came from government agencies and not straight from the military. This can be good and bad as sometimes you get a truck from a rural fire department or agriculture department that did nothing other than get it's yearly maintenance for ten years but othertimes you get one that's had a 2000lb salt hopper in it's bed since 1993 and has never been washed.
WARNING: There's a place in Wisconsin called Alfa Heaven. They advertise "good as new", "great condition", and "as close to straight from the factory as possible" CUCV's that have pretty paint and big tires...they're liars, cheats, theives, and it's been documented so AVOID THEM AT ALL COSTS.