Find a club near you using this search tool:
Regional Club Directory - The Labrador Retriever Club, Inc.
Each club's website should have a directory with some websites or even litter listings. You'll have to go through each and see if they have pups available and make contact.
You will be looking for someone that does something with their dogs and does all the recommended clearances.
This link might help too: Selecting A Puppy - The Labrador Retriever Club, Inc.