Common sources for brewing salts?

Anyone have some good "every day" places to buy the commonly needed salts?

CaC03 (Chalk) - - can I grind up plain old white blackboard chalk? It must have some fillers in it... maybe nothing that is harmful?

CaSO4 (Gypsum) - - This is common and should be cheap... but where to find food-grade? I know I can't just grind up drywall... it has other nasties in it too.

CaCl2 - - Are there common uses for this chemical that make it available?

MgSO4 (Epsom Salt) - Easy to find in most pharmacies.

What about food grade HCl or Lactic acid to adjust residual alkalinity?

HCl is sold as muriatic acid. But I wouldn't bother. It's nasty stuff and lactic acid works too and is much safer.

I second the setiment in the other thread that you should buy brewing salts from a home brew store. Epsom salt, table salt and baking soda can be found at the grocery store, though.

Kai