Where can we find staples for old Duo-Fast Gun Tacket CT 859 in Canada?

https://www.toolsadvisor.org/how-to-load-a-duo-fast-staple-gun/

at the back on the lower rail there is a thumb release.
push in/up/down and rail spring will come out load with duo fast staples 1/2 way. put rail spring back in. squeeze stapler and bang your good to go.

Duo Fast 5018C 5000 Series 20 Gauge 1 2 in Crown 9 16 in Leg Fine...
go there:

Nail gun depot (NPG)

Toolbarn.com

jl open up the slide ,there is a spring end that pushes the staples into the head ,that sticks in the rail a small screwdriver will release it,it will get stuck again but now you know the prob.

kathleen lay the tacker on its side ,head to the left ,take out 4 screws remove cover ,there is a thermo fuse lower right .you can test it with an ohm meter . most likely the problem,if not welcome to the duofast demon within. iv\'e had my tackers for over 30 yrs you need 3or 4 of them to keep one operating. also finding parts for older ones is proving to be differcult. i think they want us to buy the new ones. hope it helped jimmy c

The following staple references are still widely available and should fit your gun: 71 series, S3G, JK670.

http://www.staples.com/Swingline-Heavy-Duty-Staples-1-4/product_504225

I’m happy to help further over the phone at https://www.6ya.com/expert/jeremy_69f3cc28d95bf514