Rem did make longer barrels, and they should found for sale online if you look, however, the costs of them might NOT be worth it to add one,a s last I seen them for sale they were almost 400 bucks for a 28 inch barrel
and for that price you can buy yourself s used shotgun, and have two guns over just one!
so might just be better off buying another whole gun, than just having this one with 2 barrels!
with all this crazy corona crap going on, finding a used barrel might be hard as well,a s most OEM's are struggling to keep up with demands and are sticking to making things for there better sellers, like say rem 870's over the more odd ball models they have that don;'t sell as many !
and the aftermarket dept, really hasn't taken a big shine to the 887's either
I am sure there are a few out there that make one for it, but again due to no ta huge seller, the costs will be way higher than for a gun that is more popular
sorry not what you maybe want to hear, but its the best advice I can give you here!
NOW you can still MAYBE get lucky and find one USED too by searching on line
I found this one really fast on E bay for 200 bucks?
https://www.ebay.com/itm/20358063122...IAAOSwntdhJqHW
so maybe keep looking till you find one you feel fits your needs and is worth your costs, if buying a second gun doesn't appeal to you
a decent used 870 or like should be had for about 250 bucks, and again, then you'd have two guns over just on with 2 barrels!