Add a printer via Control Panel and then select printer type, i.e. HP, Canon, etc.
This hasn't worked since day 1 - You can only add from list already included. I have had success using a generic type printer. Hopefully MS will get the Windows Update actually working.
Very Frustrating.
Perhaps MS hasn't enabled that driver list through Windows Update yet, it may not be ready to filter for RT. There are other things missing from the desktop side that don't apply to RT, why bother to keep that button if there isn't a requirement of it.