Completely separate companies running two competing chains of real he-man guy stores in Wisconsin, with hunting and fishing supplies and tools and Bag Balm and Teat Dip and you-name-it. I've been told they at one time they were a single company run by two brothers who got into a fight but I haven't found anything to support that bit of Local Wisconsin Folklore. On the other hand, both chains are celebrating their 50th anniversary, which seems kind of odd if they didn't start out together. The Blains chain is "Farm And Fleet", whereas the Mills chain is just "Fleet Farm", with no "And".
If you are training to be a spy and your cover story is that you are from Wisconsin, this is a little bit of Wisconsin Culture you need to know.