The "sproket" is, I think, the rear bush that supports the part of the mod that sits over your barrel. With the screw thread on your barrel, that gives two support points for your mod. They should be readily available, your local gunshop should be able to order the correct one for you if they do not have it in stock.
If not try this link; http://www.reflexsuppressors.co.uk/
Atb, ft
Thanks flytie thats it alright thanks for the link, work computer wont open it so will check it out in the morning when I get home.