As of 2015, the Government Liquidation website auctions a variety of 6x6 trucks online. Its inventory is constantly changing, and mainly features military-grade vehicles. Auctions typically last for three days, and the buyer is responsible for arranging shipment or pickup of the vehicle.
Not all vehicles available for auction are military, but the vast majority are. Not all trucks are in working order, and their condition is not guaranteed. Arrange for inspection of the vehicle in question where possible. Types of trucks vary in availability, and dates of manufacture range from the 1940s to current times. Inventory is updated weekly, and part of the profits goes to the US treasury.