You might try the Petfinder website, that's where I found both my dogs. Max, the yellow lab, came from the Cincinnati Lab Rescue and lived to be almost fourteen. My current boy, Newlie, came from a rescue group in Kentucky called Let Them Live. I have had him almost three years so we think he is around five years old now. Newlie is good with people of any age and trustworthy with kids. He used to be reactive toward some dogs (if he felt they were challenging him) but I haven't even seen much of that lately. I don't know about whether he is working line or not, but he has been an absolute peach, as was Max. I am attaching a picture of him.
The website does allow you to filter your choices by a number of factors: distance, breed, age, sex, etc, plus usually gives you a little description of the dog.
Good luck with your search!