Well, Hoppes should make a brush for their kit.
Try Cabelas or Elwood Epps or any other of the site sponsors.
Sorry I can not help you with further options.
Hell if you where within walking distance I have 12 bore brush might work for free.
Didnt the kit come with an adapter for shotgun brushes?
Should be a aluminum bit that screws onto the cleaning rod????
Look it up on the internet...the kit that you have.
There shouldnt be to many kits made by Hoppes and able to figure it out fron there.
EEasy Peazy your almost there.
Rob