Not super-local (they're in New York), but you can get various cuts/types of lamb from the Eight O'Clock Ranch at Good Health in Hanover and Quincy. They also have meat CSAs and various ordering options on their website, which I believe is www.eightoclockranch.com
We've done their CSA before and it really is wonderful. I always forget to renew in time so we end up buying a lot of their stuff at Good Health. Eight O'Clock, Plato's Harvest (chicken, beef and sometimes pork) and Oake Knoll (beef and humanely-raised veal) are about the only places I buy meat.