I have seen a bunch square body trucks on govdeals.com this past month or so. Anything from a C-10 to huge tankers.
Its a government liquidation sight so You can usually get something for a good price also most local and state agencies are clearing out their lots which include lots of square body trucks.
Here are a couple Listed right now in Missouri
Free to sign up and bid on stuff. I buy stuff off here all the time.
https://www.govdeals.com/index.cfm?f...1L00g.facebook
https://www.govdeals.com/index.cfm?f...3rZ_8.facebook