Barring that, there are quite a few service march medleys that are achievable.
If you have a few GREAT players, try doing the Wilhowsky "Battle Hymn of the Republic." Put the majority of your group on the second/third(/fourth) parts and put your top top kids on the firsts. Range and endurance is an issue here though.
Also, R.W. Smith has a few patriotic medleys that are worth doing - once.
If you want a REALLY good list of medium to medium easy patriotic songs, check the Association of Concert Bands Repertory list, where they list performances by community bands. Find any June or July concert from a local community band. If you're not an ACB member, find a local community band member who is, and have them do some research.
Also, many community groups publish their programs on their websites. If you don't know any community bands, check the Dallas Winds page. They maintain a list of community bands.