Long story short, ALL modern ammo of this caliber is either API, or APIT, which is prohibited in Canada. There are only 3 ways that you could get a sizeable quantity of ammo of this caliber in the country (legally).
Method one : discover a large, long-forgotten Russian/Soviet ammo dump with crates of the stuff dating back to WW2, when the most common round was the typical AP/ball. Such a dump probably exists, as the Russians/Soviets have always been notorious for "misplacing" arms caches, getting it approved for sale in Canada by NRCAN is another story however.
Method two : purchase a lot of surplus virgin brass from a current ammo manufacturer that makes the stuff and get it here, but then again, ain't got no primers, nor powder, nor bullets. So you pretty much would purchase a couple million paperweights. I can't see anyone in their right mind experimenting with powder loads of that scale, with rifles of questionable metallurgy.
Method three : Find a 5th world metal recycler who disassembles these things for the brass and purchase said brass from them, but you're stuck with the problems listed above.