You don't need to re-register anything, the green card was a proof of safety inspection, that went out the window in July of '08 if I'm not mistaken.

4. I lost my Michigan pistol registration (Safety Inspection Certificate). How do I go about getting another one?
The Safety Inspection requirement in the law, previously MCL 28.429 has been repealed. As long as the gun was previously registered in your name and is on file with the Michigan State Police, you are not required to complete any additional paperwork. It is not a requirement that you carry your Safety Inspection Certificate or License to Purchase on you when carrying, using or transporting the gun, once 30 days from the date of purchase has expired. There are no Safety Inspection Certificate forms available to issue you a new one. You may contact your local law enforcement agency and request a copy of the information entered in the pistol entry database relative to your registration/license. They may charge up to $1.00. Or, you may make a request through the Michigan State Police, Freedom of Information Unit, 106 West Allegan, Lansing, MI 48933 for a copy of your registration.