These teams usually hold tryouts in the Fall and/or they'll hold indoor winter workouts over a series of weeks and then will pick their team after that - and usually will have a core set of kids coming back so they'll only need a few players. That being said, if he's a pitcher only it should be a little easier to find a spot.
Do you know what the top organizations in your area are? You can call or go to their website to see if they are looking for players. There may also be an online resource for you to check. In NY we have the nybaseballnetwork.com site and they have a tryouts listing. A quick look showed lots of teams posting tryouts recently. Maybe there is a similar site in Mass?