In Device Manager/ ports
Click on + (Ports COM + LTP) and expand list.
Click on Port Settings tab.
Click on Advanced button.
Use the Com Port setting "Down Arrow" to expand list of Com Ports.
You should have COM1 - COM256 listed.
This allows you to change the port number that is assigned to the port. For example, if you have three modems connected to COM1, COM2 and COM3, and you want them all to use COM3, change this setting to COM3 for ports COM1 and COM2. This will force each modem to use COM3.
See if these lead anywhere?
HKEY_LOCAL_MACHINE\HARDWARE\DEVICEMAP\SERIALCOMM
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Ports
Search the Registry for COMn (n = number) and see what else you can turn up.
If you device is an USB Printer it may be assigned a Virtual Printer Port for USB, found under the Ports tab of any Printer listed in Printer and Faxes.
Overview of the COMDisable Tool