yeast - Sources for common laboratory Saccharomyces strains?

One very important resource is EUROSCARF. http://web.uni-frankfurt.de/fb15/mikro/euroscarf/

It is one of the very famous and dedicated strain repository for yeast (S. cerevisiae) strains. You can even find some very useful yeast plasmids here.

Another resource I would recommend will be the original labs, which made the mutant strains/plasmids. Yeast researchers as a community are very nice, I have almost always obtained the strains and plasmids that requested from the original labs.

Hope it helps,
Cheers!!