The scouts need to wear the uniform when they travel in order to be insured on the trip.
My son was in a fairly large troop, and some of the mom’s organized a annual uniform shop - outgrown uniforms were donated and sold for a small amount that went to the troop.
Check with the scoutmaster.
Already have checked with the scoutmaster, that is who loaned him the uniform he has. That was the only one in my son’s size they had.