Are your tanks O2 Clean, or do you need banked nitrox?
To start. Mass Diving and Northeast Scuba do bank; as does East Coast Divers I think. Last I saw they were all a little on the pricey side.
Discovery Diving in Atkinson NH does partial pressure. I think I pay $11 for my 120s; he needs a couple days so I don't get over there much.
Aquatic Escapes in Londonderry is where I generally go now. $.12 cu/ft for banked nitrox, $.20 for Oxygen, .09 for hyperfiltered air.
I know there's a bunch others, but there are also a bunch of others here that'll answer too.