Why not just place an ad in some of the local newspapers in the Dakotas, Montana, etc and see if some of the local farmers go for it. Tell them you will eradicate their pests for free or even pay them a reasonable amount for a couple days shooting. Some of these guys get to town about once a month and are glad to know folks are coming their direction. A couple of phone calls, shack up in their barn or in your own tent and shoot for a week. It's also a great way to find the inside track on some other hunting opportunities - pheasant, deer, etc. - as well as fishing places.
The other option is to take a week's scouting trip and talk with some of them. I know a couple of guys here who did that several years ago and spend 2 weeks a year shooting at several different farms waaaaaaay out in the country. The locals love to see them, because they have enough farm chores to keep them busy without shooting prairie dogs.
ERRainman