You hear all about these Enclaves that survive out in the wilderness staying hidden and out of harms way, and chances are you wont see them because they stay out of sight etc... but Im sure there would be some dotterd groups that have managed to fortify there position away from the DMC, maybe not to the extent of Zom-Zoms on an account of labor available, but I am sure there would be some in the various old civilized parts of the world scratching out an existence.
I suppose my idea is that of having small shanty hexs dotted around Michagan representing community's that trade for stuff from you, like food or clothing and will occasionally give you a "quest" for an item, like medicine or other supplys. They may have some looters that collect junk and bring it back to the Enclave.
If you piss them off some how, like threatening, stealing from them, or attaqcking there looters, a whole bunch of angry looters will come and try to bum rush you in retaliation. There loot would not be as good as the sprawl market place, but they may offer something to interact with.