Pink salt

Also known as curing salt. A mixture of salt (93.75%) and nitrite (6.25%). Nitrite is a natural preservative (found in green leafy vegetables) that prevents botulism. It's fine in small doses, dangerous in large, which is why it's dyed pink to prevent accidental overusage.

According to this Chowhound thread, you can buy it in San Francisco at Village Market in the Inner Richmond. However, when I checked on January 14, 2012, not only did they not have it, they didn't know what it was, and couldn't tell me if they were going to have it another time. I tried calling Bi-rite, and their butcher said they get it from Carlson Butcher Supply. Not a lot on the web about them, but it sounds like a lot of local butchers use them.