This article is from the Food Preserving FAQ, by Eric Decker email@example.com with numerous contributions by others.
From Jeff Benjamin , rec.food.baking: If there's a home brewing shop
in your neck of the woods, try there. From Joel Ehrlich ,
rec.food.baking: King Arthur's Flour. Most places which sell it for
baking identify it as "Sour Salt". From several in
rec.food.preserving: Safeway. Food Lion. Ask around.