RSTA troopers are often graduates of schools including the US Army Sniper School, Special Operations Target Interdiction Course, Ranger School, Army Reconnaissance Course, Reconnaissance and Surveillance Leader Course (RSLC), and other schools befitting a reconnaissance unit. In Squadrons supporting an Airborne Brigade Combat Team, 100% of the RSTA soldiers are qualified paratroopers.
Those are the schools you should get in. As far as actually getting into a unit, I would go to an army recruiter or try and email an army contact to find out more about it.