Remmington 870 barrel
#2
Carlsons has replacement barrels for the 870 that are threaded for rem chokes.
http://www.choketube.com/accessories...Barrels&mf=370
http://www.choketube.com/accessories...Barrels&mf=370
#3
Cabelas, Midway, BassPro, and Gander usually have factory replacement Wingmaster barrels that use tubes in stock for somewhere around $220 - $230. You can find them in 26", 28", and 30". I have put one on my old Wingmaster and am very pleased. I looked at the other brands and did not like them.