searched craigslist within about 500 mile radius religiously, watched here on ExPo, iH8MUD, and other forums, went to a local military surplus yard who has about 20 of them, non in decent shape and his prices start at $2000 (kinda crazy). Took a while but I found one. There is one on CL here in Tucson right now in original condition.
When searching craigslist make sure to try multiple terms: M416, M100, Military trailer, jeep trailer, offroad trailer, 4x4 trailer, etc.
http://tucson.craigslist.org/for/5392229931.html
Too bad you're not closer to SLC. We use a company there that runs parts to us on their flatbed and runs back mostly empty.