I was thinking about getting an extended threaded barrel from bar-sto for my Sig P239 9mm. If I do that, does it mean I don't need to buy an adapter from Gemtech and I can just attach the suppressor? Sorry for the newb question, still learning.

BTW, is bar-sto the only maker?

www.barsto.com/category_main.cfm?ID=239&cco=69

As long as you order the barrel to have the same thread pitch as what the can is threaded, you won't need an adapter.