Combine white rice flour, oat flour, tapioca starch, flax seed meal, oatmeal, 1/3 cup plus 2 tablespoons potato starch, brown sugar, baking powder, salt, cinnamon, and baking soda in a large bowl.
Mix milk, eggs, applesauce, and vanilla extract together in a bowl. Make a well in the center of the flour mixture and add the milk mixture. Stir batter until liquids are fully incorporated.
Heat a skillet over medium heat and lightly spray with cooking spray. Ladle the batter onto the pan using a 1/3-cup measuring cup. Cook until edges of pancake begin to dry, about 2 minutes. Flip and cook until other side is browned, about 2 minutes more.