They have been using carbon in bracing for many years now... Infact one of the big debates for the future will be whether amputees should be allowed to compete in the olympics on an even playing field due to the biomechanical advantages they are able to achieve with their prosthesis. Check out a quick search for AFO (ankle foot orthosis) and carbon for a huge variety of options. Not sure what kind of specific bracing your son needs, but a good protetist should be able to give you some ideas and with some hints here you could likely make somethng... I can promise medical devices pay much better than boat parts for the manufacturer!