Make a short video. Nothing fancy. In fact, the more real the better, but show his swing and few other basics. Reach out to schools. Most do not have budgets for recrutiing. Your son can e-mail coaches to find out about camps. Research on your own camps and showcases. They are pricey, so you need to carefully consider which ones match your sights.
PS Generally speaking, baseball coaches are willing to provide information and help to kids that want to continue playing. Top tier DI programs-that's a different world.