Well Ashur makes a passing reference that "Ronto" is a major military power in post apocalyptica. So either Enclave or Survivors of the Canadian occupation forces. Another possibility for Enclave hold outs is the Remains of Cape canaveral, They had to get that crawler from somewhere. There could also be more than one Enclave, who is to say they didn't split into several factions after either the great war of the end of FO2?