
There is a website where you can trace Golden Retriever pedigrees, it lists ALL Goldens ever registered with the KC. For each dog it also lists puppies sired by them etc, so by using that you can start with the sire and follow him down the liens so to speak and that might help if it leads you to a breeder who has him in their lines now. Now you have to apply for permission to use that site (You need a password and username) and I'm not sure how strict they are (i.e. if they limit it to breeders for instance, don't THINK so though) but the site is at:
http://www.standfastdata.co.uk/ You e-mail them and ask for permission, tell them why etc. If you fail, PM me the dog's details and I'll see if I can look for you.
Good luck. :) 15 is a wonderful age, my oldest Golden is coming up to 13 and he's the oldest I've had.