I know Midway and Brownells sells barrels and barrel conversions.
Barrels | Smith & Wesson M&P | Semi-Automatic Handguns
It's funny seeing you guys saying you buy from Guns & Gear in Agawam.
I'm local to them and they are my go to store, they are great people there and stand behind what they sell.
It's just funny seeing someone from Florida (or somewhere else) saying that they buy from them...