Stickers and patches are offered, but the only flag offered is for the IBA rides like Pressed Penny Insanity that require a flag present in photos.
Typically, for your personal use, with no others passed on to someone else or sold to someone else, you could probably get away with making your own small flag. However, I am not a representative of the IBA, or their legal counsel, so you might be best served by contacting them first.
@Ira may know the answer to this question.