King, Precision Arms and Gunsmithing @ King City Ontario does good work. Installed Briley thin chokes in my ASEL which work I am satisfied with. They tend to be slow however. Les Paul in Oshawa is excellent, Nick Mackinson has a good reputation and quick service. I use a gunsmith here in Alberta for opening chokes only. He does it from the chamber end - which I believe is the correct approach. There are lots of others but I have personal experience with the above and can vouch for each.