Logun carbon fiber, Weihrauch and A-Tec are all certainly worthy options. However, the most challenging part of Bangersanmash's post is pulling a young teen away from the PlayStation!
Now an air rifle suppressor is a very simple device. Perhaps you can engage your youngerster more by helping him make one? With a bit of fun and hands on experience, he might take up the task of researching and finding a second hand suppressor himself. Good luck