I see most answers saying to talk to the Scout master and search the troop closet. That has already been done and they had (1) one uniform in his size. They are going to try to find more by putting out a plea in the next newsletter...though that will not help for this trip.
I will try to answer the other suggestions individually
Would the SM let you have a phone or email list so you could send out your own plea before the camping trip? The newsletter is a pretty out of date concept these days.