My LHBS just started carrying 75% food-grade phosphoric acid.
I got a gallon jug of it for only $20 (more than one would ever need for most uses), which is pretty damn good when you consider that my LHBS tends to overcharge for EVERYTHING.
And it's a Five Star product, no less. It even has instructions on the side of the jug for yeast-washing - though my purpose for buying it was to adjust mash pH.
Given that I've never seen it until very recently, (and also because the store owner told me he'd be getting smaller containers of the product shortly), I think it might be a pretty new product for Five Star, and if so, I'd expect it to start showing up in all sorts of local and online shops.