You might look for a hedgerow, usually a line of trees between fields. A sure sign is if there are some stumps in there where posts have been cut. Osage trees grow really gnarly and twisty, with a very round shape overall. The thorns are only on juvenile wood and not terribly pronounced (unless you rake your head on one, then you'll pronounce a lot).
If you find a row, try and get suckers, that is, new trees that came up off of a cut stump. Those tend to be fast-growing, and grow taller/straighter because they are competing for light with the surrounding trees.
Also check sale barns, a lot of times guys will sell hedge posts there on weekends when there's a livestock sale. I just got a phone number for a cutter from his pile, nothing in the pile looked good enough but if you tell them what you want they might come up with something. The price for a hedge post is minimal, usually a good endpost (10" diameter, 9' long) runs maybe $25.
I live in Hannibal, a few hours away from you. If you are hard up for wood you might make it up here and we can find something. But I'm sure you'll find stuff close to where you are. My friend and I have cut five big trees and two smaller ones in the last month, I'm getting close to having everything processed (debarked, sapwood removed) and stored.