First, be sure your father-in-law wants a dog. Then be sure he wants a large dog. Labs are high energy and need lots of exercise. They are also very large and strong dogs. While it may be the breed you like, it may not be the best choice for him.But, if this is what he wants, all the advise on getting a rescue dog is good. I'd also add that you can get great dogs from organizations like Seeing Eye and service dog organizations. They place dogs that 'fail' their program. The person who raised the dog gets 1st choice, but if they don't want the dog, they have a waiting list of people who do. These dogs have tons of socialization and training. So check the web and see if there are any service dog groups or guide dog organizations near you.
www.seeingeye.org