I haven't tried this yet. I just saw the article yesterday. It might be a good article to have printed out.
Yeast is a living thing, so it isn't really good for a long time. Maybe a year.
I am a baker, but I don't make sourdough bread. I went online and got the recipe for the sourdough starter and the bread recipes. I figure that if I cannot buy yeast that I can still make bread with a starter...