Sorry, but if it's corn, it really isn't Vodka. It's corn liquor. If you want vodka, look for potatoes, or at least rye. If you want corn squeezings, look for some Georgia Moon. At least it's fresh when it's sold.
Corn liquor, if it's highly distilled and filtered, IS vodka.
Vodka is basic distilled ethanol. You can make it out of any kind of sugar/starch. You can buy a bag of sugar at the store and make your own although I don't know why anyone would bother since it's so cheap.