USAR (C-12 and UC-35)
2-228 AVN: Ft Rucker, AL; Dobbins ARB, GA; Ft. Bragg, NC; NAS Willow Grove, PA; Johnstown PA; and Ft Knox, KY
6-52 AVN: Ft. Knox, KY; Ft. Hood, TX; Ft. McCoy, WI; Los Alamitos, CA.

ARNG
Almost all states will have a C-12 for state missions.
C-12 Regional Flight Centers: Fort Belvoir, VA; Fort Hood, TX; Fort Lewis, WA; Hawaii; Alaska; and Puerto Rico
C-23's: Ft Richardson, AK: 1-207 AVN; Gulfport, MS: 1-185 AVN; Kingston, RI: F-192 AVN; Salem, OR: A-249 AVN; Marietta, GA: H-171 AVN; Clarksberg, WV: FWTS
C-26: Scattered about in various locations in the US