It isn't hard to find prairie dogs they are all over East of the front range. The hard part is finding a landowner who will let you shoot on their property. All you have to do is drive around a bit stop off in towns at the local café and such on a Saturday or Sunday morning and talk to a few people. They will let you know where you can go and who to ask. You just have to put yourself out there, expect to be turned down quite a bit but you will find some good leads.
I'm lucky I just have a lot of places to shoot them because most of my immediate family Ranches in Eastern Colorado, and I still know most of the other local farmers and ranchers. The biggest problem about where the prairie dogs are from where I live is that I can put close to 300 miles a day on my vehicle just to shoot them. At $4+ a gallon for diesel it kind of puts a damper on my shooting them.
I have a few people who I take to shoot prairie dogs every year. Generally I have to be with them if they are going to shoot, and I'm the guy who gets held responsible if something happens. Unfortunately my time that I can do this is real limited. Between my regular job, Army Reserves, and work I need to do to the ranch I don't have a whole lot of time.