Leon, we (Wildflower Soaps) sell two cornmeal soaps on the "DirtDoctor" web site in the "shopping" link. I can't give away my recipe but can possibly help you. First find a basic soap recipe that you feel is beneficial to the skin. We use a fresh goat milk recipe. You can then add horticultural or whole ground cornmeal to the soap after you grind it to your liking. We have a multi-step process that involves extraction, infusion and more. Keep in mind that this is a lot more complicated then I'm making it sound. You don't want to burn the goat milk or the corn (or yourself for that matter).
My recommendation is to start with a simple, basic soap first or buy some melt & pour from someone else and add your cornmeal to it. This is what some of our competitors do. The quality and benefits are questionable with a melt & pour, but you have to start somewhere. Check out the link below for basic instructions & simple recipes for beginners.