For high school bands, you can go to the MICCA marching band competition in the fall - I believe it's sometime in October.

There's also drum corps over the summer, which is typically college-aged performers who tour the country with their corps. There's usually a show in Lynn in July - look for DCI competitions.

Additionally, you could check the football schedules of the various colleges in the area and try to make a game where both schools have their marching bands there.