Download Scriptomatic http://www.microsoft.com/en-us/download/details.aspx?id=12028 or similar. This will enable you to search WMI and look for your IMEI.
If it's not queryable in WMI and not in the registry (remember to run a search) consider looking at another application that lists the IMEI number like a dialler or card software and look for it in it's registry location or ini files etc.
If you still can't find it, but the IMEI can be displayed on screen, you could check to see if Autoit can capture the IMEI from a label or edit box on a Windows 32bit form. You could launch the app hidden and capture the detail in the background.
It will be there somewhere if software has to use it, you just have to be determined.
I'm afraid I don't have the hardware to hand so can help no further.