Peter:
In RTMT, select the performance tab, choose your device (sub, pub), expand Cisco TFTP, and drag RequestsNotFound to the viewing area.
This represents total TFTP requests where the file was not found (including phones).
For unregistered phones, Use the RTMT Device Search (under Device). Double-click 'phone', then set criteria to 'unregistered', 'Any CallManager', and 'Any Model'.
Transient network connection attempts in EventViewer is another resource.
Hope that helps.
Tom
