national guard goes by state, and it VARIES on what openings they have. For my state, they have no openings for nurses to begin with. Your best bet is to go reserves and give it a shot.
Reserves is federal government and they have a lot more openings. You can try contact a NG state OSM or reserves you would contact a career counselor/AMEDD recruiter.
Sorry not not too much help but I figure pitch in the knowledge I know from being a guardsmen.