If the dog was brought locally you could ask for back copies of the local rag pet section, alot of working dogs aren't posted for sale as they are normally sold in house so to speak. I know my breeders went in majority to people on the local shoots.
Pity the first owners haven't told you how they found her for sale or any other details. I normally ask for info on the vets they used because most people forget the correct dob but will have supplied it to their vet when they did the jabs... very useful vets
The KC also have a list of affix holders might be worth asking their library for assistance their research staff are fantastic at tracking owners and breeders down. I've used them several times for rescues and its been very successful when I've hit a dead end.
