If you're looking for a barrel, I would suggest buying direct from the manufacture but be prepared to wait several months. I recently ordered a 6.8 SPC barrel from Stag. I'm on a 3 - 4 month waiting list. You can check with all the manufactures, DPMS sells barrels in a lot of different calibers.
What caliber are you looking for? We've had people build a bunch of different caliber uppers here so I'm sure you'll find the answers you're looking for. Olympic Arms recently had pistol caliber barrels in stock.
Welcome aboard the site. Stick around for a while. We would love to see how your build turns out.
Welcome aboard Tricky! Where are you in Dixie? I'm near Dothan and Xamraci is in the Montgomery area.
I'm fond of the 6.8 and 6.5 also. One day, one will grace my gunlocker.
Good to have you here.
-Recoil
Welcome tricky.