You can receive a coupon for a free box of Betty Crocker’s Gluten-Free dessert mix by calling 1-800-446-1898. Select option four from the menu to be transferred to a live operator, and ask to sign up for the coupon. They’ll take your address and ask three very brief survey questions. The person I spoke with was extremely nice and happy to help, and said my coupon should arrive sometime by the end of August. You may be on hold for a little while before you get through to a rep, but I just organized my email inbox while I waited!
Thanks to JANE4Girls for the tip!