In the U.S.A., the various State Guard (sometimes referred to as [insert state name] State Defense Force) units-
not to be confused with the [State] National Guard- are probably the closest thing to a Gendarmerie outfit we've got.
Here are a couple of examples:
https://encyclopediaofarkansas.net/e...te-guard-5301/
http://www.gasdf.com/
https://en.wikipedia.org/wiki/New_Me..._Defense_Force
AFAIK, most, but not all, states have such a force, but I imagine in a T2K scenario, the state legislatures and governors of states that don't would quickly authorize them.
I don't recall seeing mention of such units in any of the CONUS campaign modules, but they should be included.