I have been searching for Mossberg replacement barrels for one of my guns.
Mossberg has new barrels for sale at several retailers. Model 500 in 12ga is easy to locate and run 135 to 180 dollars ( U.S. currency). Model 835 and 590 are also available in a similar price range.
I have had very little luck finding one locally in 20 ga. You should be able to find something in 12 ga to fit your needs.
You can't fix stupid....however ignorance can be cured through education!