回复：请教 PJiang 老师: About Returned Green Card

You can complete Form I-90 and mail it with supporting documentation such as I-485 Approval Notice to the USCIS Service Center or National Benefits Center (NBC) that mailed you the card which was not received (you do not need to pay any fee for this). If you need the GC very urgent, you can go to USCIS local office in your area to get a stamp on your passport first.

See website for I-90 filing:
http://www.uscis.gov/portal/site/uscis/menuitem.5af9bb95919f35e66f614176543f6d1a/?vgnextoid=b3f7ab0a43b5d010VgnVCM10000048f3d6a1RCRD&vgnextchannel=db029c7755cb9010VgnVCM10000045f3d6a1RCRD