I havn't been junk yard diving in troll land yet, up in the UP there's not a whole lot of good yards either. I think most of them legally won't let you in the yard because of liability. Most of the "good finds" in the UP are personal collections that arn't really technically junk yards. Most of my junk comes from my buddies and their collections.
Depending on what your looking for
www.car-part.com is good for later model stuff. Also if you want to travel PM me for a couple really cheap u-pull it's around chicago. Also depending on what your looking for I might know some one that has it hiding in their yard in the UP
Classic broncos is probably your best bet for used bronco parts. Trying to find EB's, jeep's, fj40's, and other off road stuff in a big junk yard is pretty hard, they are usually rusted into the ground or a huge pile if they are there.