You know, I haven't seen root beer Kool Aid either in the store. But i have seen a generic brand of packet root beer at one of those dollar stores. I myself am looking for lime flavored, and can't find that.
I believe that Kool-Aid use to make root beer flavored powder. These days you can purchase root beer extract or root beer syrup. There is Root Beer Flav or aid available for about 11 cents a packet directly from the company. Gl.