I am looking for a dog after being a puppy raiser for Guide Dogs.

Many Guide dogs are bred as Labrador/Golden Retriever crosses (or from a heritage of crosses), ranging from 50/50, to 15/16th any many fractions in between. They are generally very good dogs, showing many of the good traits of both breeds. Guide dogs obviously breed in house for their requirements.

Do general breeders ever go down this route, or is the process only ever 100% pure bred?

My first Golden Retriever was born in Dec. 1958. She was Field Trial bred from Haulstone lines, and was the third generation from the introduction of a Champion Holway Labrador - the intention being to try to improve speed in the field. I believe that these experimental matings would require Kennel Club permission. The first generation would be classed as an Interbred Retriever. mated back to a Golden, the next generation would be a Golden Retriever, but would carry two asterisks after it's name to denote the outcross breeding. My girl carried a single asterisk, and her puppies were able to be registered as pure GR.

The crossbred puppies bred by the Guide Dog charity are registered on the activity register. This register does not need any information about the dog's breeding to be supplied, and so would not be likely to be used by a serious breeder. Field Trials enthusiasts may occasionally mix breeds, but they are likely to be high energy performers, and more demanding to live with as a pet dog.
I believe that it is possible to acquire a failed Guide Dog, but there could be a long waiting list.

I have PM'd you with the name of a breeder who regularly gives/sells puppies to Guide Dogs, she may be able to give you good advice.

There are probably people who do breed Lab/Goldie crosses but whether they are from health tested parents and are being bred responsibility is another issue entirely

Thanks for the replies. It was just more out of interest to see if GrxL were widespread in the general dog population. We're off to see a recent lab litter in a few days.