flour substitution?

I would like to make the Mock Oreo Cookies but I do not have any potato flour. Can I substitute corn flour, buckwheat four, potato starch flour or corn starch for it? Oreo double stuff is one of Evan's favorite cookies. So far the only decent cookie I have been able to make is the Dan Peanut Butter Cookie. His teacher asked me today for the recipe so she can make it for the class. --Betty Mock Oreo Cookies 1/4 cup cocoa 1/4 cup potato flour 1/4 cup rice flour 1/4 cup sugar 3/8 cup stick margarine 1 egg Preheat to 350. Grease cookie sheet. Mix dry ingredients and set aside. Beat egg then mix egg and margarine together. Mix in dry ingredients (may have to use hands). With dough form cylinder-shaped balls and put on sheet. Flatten with fork dipped in cold water. Bake for 12-15 minutes. Once cooled put frosting between smooth halves of cookies. Oreo filling 1/4 cup shortening and 1 cup of powdered sugar and mix, mix, mix. .