I've been checking eBay for months now looking for an inexpensive used 18.5" for my pawnshop steal of an 870 Wingmaster 26". No dice.
There are plenty listed, but the bidding gets silly in a hurry. By the time it's over, I could buy a brand new Mossy-made barrel. [/rant]
Just go down to WalMart and get a Mossberg for a little over $200. They're pretty cheap and very effective.