Where can I buy fresh, live yeast for making bread? (NOT active dry yeast) Where can I buy live yeast? Who sells it? Can I buy it non-commercially? Does anyone sell it online?

I've found it difficult to find, at least in the United States's grocery stores.
Another option-- if it is available to you-- is a grocery store in an area with significant population of recent Eastern European immigrants. There was a Polish store in Ann Arbor, MI (until it closed last year) where the live  yeast was available by weight (cut from a big block, of the same consistency as cake yeast).