After a quick search, I don't see barrels for sale but the bantam has a 24" barrel so maybe check with Mossberg to see if it can be purchased separately.
I sent them an email and posted on their Facebook page. Still waiting to hear back. I will probably call them next week if the don't message me back.Admittedly, it has been a while since I looked for anything for my SA-20. At one time I fancied a pistol-grip stock but found it was made of unobtanium. Common consensus is that Mossberg (Int'l) stocks NOTHING for these which is a shame... It could really be a popular gun, if they did. The Weatherby SA-459 is VERY similar and also made in Turkey by the same MFG, (I think).
Dumb question, but did you try calling Mossberg direct?
Btw, Welcome Aboard, Ski!
I called, They don't sell the barrels separately.
Thanks for the update. There is Joe Zakher at Mossberg that you might try. I don't have his contact info handy but you might try a search here at MO or someone may have his Email. He has been helpful when possible for questions like yours... Good Luck and keep us posted.
Choate makes a +2 and +3 extension for the SA-20--I have a +3 on my Thug. Search my handle and "SA-20" and the thread(s) should come up. About $60 shipped.