You wont find a good aftermarket choke in Canada and you'll have to order and buy from the USA. For that gun of yours you need a .555 in an Pure Gold or Indian Creek. If you order one from the USA ask to have it shipped Ground USPS and you should save on the duty.

There are a number of places that sell Hevi shot Hevi 13 #6 in 3 in

It would help to know where you are located...