If you're interested in the body only, try contacting Kevin at Missing Link Resin. The styrene body (only) can be found in the current Mustang II kit. Kevin can sell you the Cobra bits:
Also, there was a complete Cobra II kit by MPC. They pop up on eBay quite often.
For the best Cobra II decals, contact Keith Marks. His e-mail and Fotki address is:
Guys, I had to change my email addy to email@example.com, thanks
Kevin Missing Link resin cast