Does market basket sell pork belly?
I'm looking to make chow's pancetta.
They do sell it, but at least in Somerville usually its already sliced (and often bone in) so you would need to find a butcher to request them to get you a whole or half belly, boned. Blackstone always has it in half-slabs. McKinnon's you should be able to call in an order and there are many other places.
Super 88 and most Korean groceries (Mirim in Allston, et cetera) sell sliced boneless pork belly.