If the reciever is fine, and the barrel is bad, Remington makes plenty of extra barrels for 870s. I own three. They are availible online withot the need for a FFL. Ebay has plenty. Contact your local Remington dealer for new.
BTW, I own:
20" Imp Cyl Slug barrel (self def)
20" CUSTOM Full Choke Sighted Barrel (Remington ony made a few for the NYS Troopers
24" Variable choke barrel w/ three choke tubes.
If you're using the fun for hunting, the variable chokes are awesome.