Shoots, you'll be missing the Waikiki uke fest by a month. Oh well, plenty else to see. There is no lack for ukulele shops on Oahu, especially along Kalakaua Ave in Waikiki. IMO, the best of these is either of the two Ukulele Pua Pua stores. They carry an amazing array of ukes of all makes and showcase many of the state's best custom builders as well. Also, several of the the "Big K" companies offer tours or will be happy to show you around. You may want to call ahead to make arrangements. have fun.
Aloha, Chuck