If it's a matter of just trying a few things to see if he's inclined to go in that direction, I guess I'd think about contacting other schools in the area (possibly with the help of his music instructor or band director) to see if they have other instruments that he could just try out for a day or two, or even just try out under direct supervision of the band director who has them. Or maybe contact some community or New Horizons bands to see if members would be willing to let a kid try some instruments they own.
Gary Merrill
Wessex EEb Bass tuba (DW 3XL or 2XL)
Mack Brass Compensating Euph (DE N106, Euph J, J9 euph)
Amati Oval Euph (DE 104, Euph J, J6 euph)
1924 Buescher 3-valve Eb tuba (with std US receiver), Kelly 25
Schiller American Heritage 7B clone bass trombone (DE LB K/K10/112/14 Lexan, Brass Ark MV50R)
1947 Olds "Standard" trombone (Olds #3)