By NATO matches, I assume you mean the life boat matches with the big 1" head on them?

If that's the case, I've had some that are easily thirty years old and they are still fine. Every few years I have cause to use one and they don't crumble, light up as they are supposed to.

Who knows maybe the quality of them was better back then. But in all, they have not deteriorated to any appreciable degree.

As to where to find them in Canada, hhhmmmmhhh. I think I may have noticed them at Pay-More (Save-More) in Toronto a while back. Not certain though. Have you tried all the surplus stores in Montreal?