I figured I would post this here instead of a PM in case any one else moves to the area. Welcome to boston CC!
there are a bunch of great pizza ingredient spots around the area. My favorite place to get anything fancy for making pizza is http://www.salumeriaitaliana.com/
in the north end. They even sell caputo flour. Fresh cheese in the north end makes some good fresh mozzarella, carries lots of imported italian ingredients, and also makes the best italian sub around with their freshly sliced meats. If parking is too tough in the north end you might also want to try http://www.caponefoods.com/
in somerville. they have caputo too, but it doesn't quite have the turnaround of salumeria, so stuff like buffalo mozzarella is not as fresh.
If you are interested in larger quantities of just about any high end italian ingredient check out http://www.accardifoods.com/
This is where I buy my 55lb bags of caputo, high end olive oil, cases of smaller cans of san marzano tomatoes, 50lb bags of king arthur sir lancelot flour etc. Their goods are only available by the case, and I always try to buy more than just a bag of flour so that they don't mind selling to me the next time I show up, as they do try to discourage cash and carry.
Its tough to find 6 in 1's around here, but Just about anything else can be found in larger quantities at costas provisions, who are happy to do cash and carry. I find that tomato magic at costas is almost identical to 6 in 1's.
Grande fresh mozzarella is sold in smaller quantities at Bovas bakery in the north end. Normal aged grande is tough to find around here. They have it and some good flour plus Stanislaus and Escalon tomatoes at New York supply, but wont break a case. The only place I know of that sells it in small quantities is at a place called Fulciniti's Market 121 Hammond Street in Waltham (781-893-2276)
If you want to buy individual cans of tomato products including many of the top names like stanislaus, redpack, hunts, and furmano they have them along with a decent flour selection at food pak express. They specialize in asian ingredients, but this is the cheapest place I have found for restaurant supplies and is where I get all my peels, cambro containers, pans, cutters, knives, ladles, sea salt by the bucket, cutting boards etc. They also offer a discount on their already discounted prices if you become a member (similar to costco,BJ's etc) but this is not required to shop there. They are right next to newmarket square at 120 southampton st. with entrances to their parking lot from both atkinson st and topeka streets. foodpakexpress.com
Oh, and if you go to newmarket square (costas, new york supply,foodpak) You HAVE to go close to lunch and try speeds hot dogs. Totally amazing, probably one of the best hot dog in the US. This crazy hot dog truck steams Pearl brand hot dogs in apple cider, swabs them with a home made BBQ sauce (including small bits of fresh fruit!) chars them on a charcoal grill, and tops with home made chilli, vadalia onions, and a secret mustard blend. I know It sounds too sweet or topped, but its not, you wouldn't believe how good they are. The only downside is that they are HUGE, almost like a hot dog sub, and cost 8 bucks.
Good luck, and I have more....let me know if there is anything you cant find.