Surprised you haven't found any in AZ. Not even http://www.dvap.com ? This guy knows folks in North Dakota, and from cruising ND from the East to the Southwest corners, I can tell you, they've got some great barnfinds. I'd guess that SD would be likewise. Anyway try this guy. We're about 1,900 miles straight North of you. He's about 100 miles west of me. http://www.callingallcars.ca/
I don't know if KIJIJI has a statewide search function or not, but I'd really grab a map and check out the larger towns in SD, ND and Montana/Idaho. The thing is that roadsalt doesn't work below 15C (5F), so for 5 to 6 months of the year, these colder states don't use it. Besides, most of them didn't start until the mid-60s. You'd probably find all that you want and options you never heard about. Heck maybe even a Hearse with power windows.
