I've heard from a friend in Vaughan that he gets them at Costco, but he may just be getting flats. I'm sure with all the BBQ restaurants starting up in TO, a decent butcher shop will either have packers of various weights, or can get them with a bit of notice. Try Kensingtom Market Or St Lawrence Market. There's someplace in Parkdale too, but the name escapes me.
I moved to Huntsville 10 years ago, but I still work in the city 4 days a week. I got my last 2 8lb briskets from a guy in Gravenhurst. I did both on my 22.5" kettle, and they turned out mighty fine.