Grabbing a prepaid T-Mobile 1616 for $20 at 7-11 will be a far less grating experience than trying to get a sim out of a mall kiosk.
Generally, the only place where you can reliably get just a SIM starter kit (you need a kit with the activation code not just a SIM) is at a corporate store. Unfortunately, unlike in Europe you can't just go into any convenience store and get a starter kit.