ISO: The perfect sausage pepper and onion roll
You might want to try Quinzani. It's mostly a wholesale type of place, but you can walk in and get anything retail.
Their regular sub rolls are pretty standard soft stuff. What they call "Panini" has a longer ferment and a bit of semolina or cornmeal on the crust. I really like it. Then you could go with the big ones and cut them to meet your needs: french bread (which you see bagged up on your left as you enter), French bread for subs (not on display usually. same recipe but cooked less.) And "baguette", not like a real baguette but really good - more crusty than their french bread.
Do they use the Piantadosi rolls? If so I have seen them I think at Roche Bros in W. Roxbury, in front of the deli. I here you on struggling to find the right kind, to crusty or hard a crust, and the sausage shoots out like a torpedo, to little tooth, and it turns to mush. Sandwich's are such a delicate thing