Mekong Market on Main Street is an Asian market that always has fresh pork belly available, and usually duck. If you ask at the fish counter they'll find the butcher and he'll get you whatever you need.
Leroux's meats in Holden MA? I don't eat meat but know the family and would suggest you give it a go. Mom loves their Polish sausage. She also goes to Tom's on Water Street I think? Fairway Beef is popular.