I've bought tons of mags shipped from US. CZ and P226 and desert eagle. After shipping costs, crazy exchane rate and the occasionnal taxes, they end up about 1/2 the price of buying them in Canada. I also got magazines that are legal but very uncommon in canada, like 10 rounds 1911 magazines. They seem to never run out of mags for the most popular stuff like CZ75, 1911, P226.
I get them from brownells, they fill all the state department export forms so no export problem, and they will only ship magazines that are legal in canada. So if you buy, say, a 10 rounds pistol magazine, you'll get an actual factory 10 rounds magazine, not something pinned to 10. That's much better imho, as sometimes the guy who pins the magazines places the pin a bit too high, like it's pinned to 9.9 instead of 10, and then it's either super hard or just impossible to insert the 10th round. As far as I know, their website will outright refuse to sell you a 14 or 17 rounds mags or anything that's not canada legal.