Yeah. Nordic Components is what you want.
Tactical Ordnance is the only Canadian dealer that I'm aware of. But they're great to deal with.
Are you running a 28" barrel? If so; The +7 extension is what I have on mine. It now holds 11+1 shells.
The tube pokes out about one inch past the end of the barrel. For my tastes; that is perfect.
If you hate the look of a tube that's longer than your barrel, just get the +6 extension.
If you want to go all out on capacity; You can get the +9 extension.
Just be aware that it will be seven inches longer than your barrel, and can be quite challenging to run with.