Was it missing from the kit? If so, you can contact firstname.lastname@example.org
with a link to this thread and we'll send you one.
Otherwise, you can easily make one from 2 1x3 pieces of breakaway header soldered next to each other. We don't have the 2x3's for separate sale, but we do sell 1x36 breakaway strips.https://www.adafruit.com/products/392