Baking powder usually contains cornstarch. For those who are also corn-intolerant, you should note that there is a brand that does not contain corn, made by Hain Foods. It’s called Featherweight Baking Powder. It is gluten free, corn free and sodium free. If you cannot find it locally, you can order some on Amazon in sodium free or low salt. Note that they do not guarantee against cross-contamination of corn.
Another option is to make your own.
Adjust amounts as needed. I suggest making a large batch to keep on hand, using one baking soda to 2 parts cream of tartar. You use 3/4 of this mix to each portion called for of baking powder in a recipe. For 1/2 teaspoon of baking powder see recipe below: