A couple suggestions:

Valor - Larry Clark
March of the Syncopated Penguins - Rutgers

Something you might consider is finding a march that's written in 'flex band' format. I'm working on one with my NV group that works great with being able to alter the parts for the kids that way. I am working on one called Bravo Zulu with my kids that is coming together pretty well due to that flexibility. You can't do it for PML pieces, but a march of the directors choice allows that option. Might be worth searching the flex band part of Pepper some too!

Best Wishes!