If you want to do rotations at a military hospital you must either:
A. Join the military and do HPSP (the military scholarship program)
B. Go to a school that has a contract with a military hospital; therefore, they require you to rotate at a military hospital.
I actually rotate at an Army hospital during my 3rd year (I was there with surgery, those guys are hardcore) but that is because there is a stinkin' huge Army base here where I live. Speaking from experience as a military brat with a father in the medical corps, it would be very hard to rotate at a military hospital "just because". Even with other hospitals around the country, applying for away rotations is just that...an application process. I'm not sure if the military offers that at all. I'm not saying don't try, (it never hurts to ask) but rotating at a military hospital is really for people who are interested in the military, so that's who they'll give automatic preference.
Hope that shed some light. 😉