Alex, If you're a student at Algonquin, OttawaU or Carleton you can get full access to liquid nitrogen for experiment purposes.
There is also a Liquid Nitrogen plant off bells corner's but I don't know if they sell to the public, always a great idea to swing by and have a chat with some of the workers.
If that didn't work I'd try at a car shop.....
I've been looking for the substance for a long time as well.
I know for a FACT they sell it on the shelves in Brownsville, TX. So if you can get it shipped to you, that would be the easiest !
Hope this helps you out Alex, and for anybody else to read this.