Robin I can tell you that I wasn't able to find Rooster Booster (same thing) at any of the farm stores so what I am leading to is either MFA or WAlmart is your choices. MFA wasn't open on the day that I needed it so not sure they carry it either.
Another good suppliment to have on hand is Red Cell. It comes in gallon or quart jugs and is with the horse supplies. Since it is high in Iron it just takes a couple of drops a day for a chicken.
Our Atwoods here has the Rooster Booster. Manna Pro has a good suppliment out for poultry as well but man is it high. In the big bags it's around 35 or 40 dollars a bag. Good stuff though and we have raised a lot of calves on it.