Hero Surplus, Oshawa ON. 905 721 2500 10 or 11 bucks. Not sure if it's on their web or not. They sell a lot of Magpul, King Armoury.
They also sell airsoft/paintball, so make sure you get what you mean to get not some plastic Chinamese paint ball accessory.
Slightly awkward to install as it can't be screwed together and installed, then tightened. You have to separate the stud and nut and install. I just held the nut in place with my pocket knife and screwed the stud in, no problem.
