Snapshot would be my first call.
they are listed on Ruger.com but its a coin toss if they would actually send it north - they seem to be pretty hit or miss on what they will ship, usually if it has anything to do with the gun itself they wont and will pass on to Snapshot.
that said i have gotten stuff off them before, keep in mind they only ship to Canada when they get enough stuff to make it worthwhile, so expect a month delay in shipping if my last 3 orders are any indication.