Hey Aeris,
I don't know about Canadian breeders, but I'm sure you'll get more help in this regard. As was previously mentioned, most breeders have their snakes in brumation right now and will breed them once they awaken. Then you're looking at roughly 100 days (depending on species and temperature) before the babies are born. In the mean time, you might have a look at
Kingsnake.com Classifieds > Canada - Snakes. There are some advertisements near the top of the page for breeders, and they may list garters for sale on their web pages. There will be a lot more snakes available this spring on this and other websites, though.
Rick