You might want to check out the HID lamps offered by Xsighting Lighting:
http://www.xesighting.com/hotrod.html
Xsighting's parent company is Valeo Sylvania, who makes the OEM lights for the Shelby GT500 and a bunch of other OEM applications.
They have several different round lights that should work for a Cobra. These are real HID lights, not some drop in blue bulb.