If you don't need strictly kosher, just kosher-style, Nortown has a great selection and will cut to fit your needs…not as expensive as Hartman's. Other than that, for strictly kosher, try the Sobey's near Yonge and Steeles.
I've bought a few non-trimmed briskets at Kosher Toronto. They will also split the point and the blade for you if you don't need a full brisket. Not cheap, I assumed they would discount the brisket since there was no butchering involved I was wrong.