ANG C-17s:
Jackson, MS
Memphis, TN
Martinsburg, WV
Stewart, NY
Hickam, HI (joint unit)
Anchorage, AK (joint unit)
Charlotte, NC (coming online FY 17)
Pittsburg (strong rumors)
C17 Reserve units:
Charleston, SC
March AFB, CA
Not as familiar with other aircraft. I know there are ANG KC 135s in Knoxville, TN, Birmingham, AL, and Meridian, MS. As you mentioned, there is also the Reserve unit at Macdill. Good luck to your son!