Barrel lenght does not matter with modern powder (the Choke is were the patern comes from)it used to take a long barrel so that all the powder would burn before the shot came out. now i beleive they say all the modern powder is burnt within 16" of the barrel.
I have a Bennelli with a 21" barrel that paterns better than my 1100 with a 34" full trap
Cabella's and Bass Pro bothhave 1100 barrels that are standard any choke or lenght you want or with rem-choke
you also might check in your local gun shop they may have a used one for less