Are you looking for "commercial" lead, or looking for a place where you can buy pure (or as pure as you can get) scrounged from a scrapyard lead?
I don't know of any specific places, per say, in Alberta, but I would check out a scrapyard or two in my area. That's what I've done in the past, and will do in the future.
Plumbing lead and roofing lead are pretty good sources for pure lead, so if you live in an area where there's renovations going on in older neighbourhoods, chances are you'll find one or the other.
Couple of years ago there was mention of redoing the plumbing in the historic part of Brandon mb, because of all the "old lead pipes" in the area. If I lived closer to Brandon, I would have gone scrounging, by either talking to the work crews, or talking to the local scrap yard, or both. Sometimes the foreman will let you take away the heavy scrap, because they pay by the pound for removal, and some guys are pricks about it. Depends on the guy.
Some guys have a doctorate in scrounging, others, not so much.
I wish I was more helpful than this.
How much lead do you need?