I'd stick to a factory Remington barrel. Any more it is not really cost effective to buy additional barrels. For just a few dollars more you can buy a 2nd gun.
You could always look for a cheap beater in a pawn shop and cut the barrel down. It ain't rocket science and I've done several with very good results. If it has a vent rib you cut on the rib post. You have the option of cutting at 21" or 19". I cut at 21" in case I mess up. If I do I have one more cut and still be legal. I ended up liking 21" better anyway. Then I added a fiber optic sight that clamps to the rib.
I've used these before with excellent results with both slugs and buckshot.
https://www.midwayusa.com/product/31...nd-green-front
Would be a lot cheaper than buying another barrel.