Tats is talking about labmed.ORG; click on: http://www.labmed.org

Click on Lab Links to get to their link page; scroll down about half a page and click the Lab Rescue page.

And you can try a generic search engine - try almost anything that comes to mind (rescue, shelter, lost) +Dog or Lab and you'll get more hits than you can visit. Most every state and large US city have a Lab rescue or owner's club that will jump for joy to help you find another FurKid.