there are 4 JROTC branches in the US... Army, AF, Navy, and MC...
Marine Corps programs are scattered throughout the country, I think there are 15 in all. I tried to get my school to do it, but getting JROTC in a school filled with anti-military liberals is really hard...
If you want a marine corps program do this... write up a proposal or survey for your school saying that you need people interested in the program to sign it. Try to get 100 signatures(the JROTC HQ requires 90, but just go for extra), and if you do, take the signatures and proposal to your principal and have her/him look over it. I'd suggest coming up with a good speech or something like that to persuade the principal. If you manage to talk him/her into sending the proposal to the branches, then good job, you've made a difference in your school. If not, then oh well, wait till you can join the real military.
The reason I focused on the Marine Corps for this is because I tried this already with that same branch, but I failed to even get 50 signatures(50 is the minimum number of cadets that must be enrolled in the program for it to stay active).
I guess that's it.