Have you considered .. teaching them the music through tutorials, sectionals, and the like?

I was a one-man-show 2A/3A school for a decade. I regularly put kids in the top half of their sections and had area qualifiers because I made it a point to the kids that they needed to work on the music. And not just color instruments - I qualified trumpets, horns, flutes, clarinets, saxes - all of it. Middle and high school both.

You're not competing with those 4A schools. There's an entire band track for 3A and down. Kids can advance even if they don't make Region.

It sounds like you're prioritizing marching band over region band. Find a way to do both. Practice the music earlier. You know what next year's music is RIGHT NOW. Hand out the packet before they leave for the summer.