Your IMEI is in hardcopy inside your phone, as well as available by the phone's original software. I don't know why it didn't survive the upgrade to Cyanogen Mod -- you might search the xda-developers site for some discussion.
In the meantime, you do have access to your phone's IMEI. Open the back of the phone, take out the battery, set aside the battery and the cover. There is a white identification patch beneath the battery. Get a magnifying glass, unless you have great eyes. Look at the block of material that is centered, in the lower half of the patch. Your IMEI is there, permanently, unless the phone has gotten wet.
The IMEI is the top line of numbers over the top line of bar code. Very carefully, using the magnifying glass, copy the IMEI. Or, if you have another phone with a software barcode reader and camera, you may be able to get a reading of the IMEI in the back of *your* computer without getting upclose and personal with a magnifying glass.
Best,
Soycoffee