Looking for a good supplier of earth pigments. The 3 colors that I am in need of are: Lamp black, Burnt Umber, and Venetian Red.

http://www.realmilkpaint.com/powder.html lists earth pigments for sale.

http://www.milkpaint.com/ does not specificly list them but they may be hidden somewhere on the side and I didn't see it.

Woodcraft and Rockler sells milk paints as well and should have then in stock in your local store but I'm not sure if they'll have the specific color. They may have something that is what you're looking for but just called a different name though.