Our last puppy, a working labrador, did not come from a known kennel so to speak. We found him this way: looked up many different gundog kennels websites until we found perhaps 10 or so that seemed to match with our ideas. For us this was good, successful working dogs that lived in the family home and did other activities than working, medium sized, much emphasis on temperament, not many litters, low inbreeding and health test results of all dogs and bitches freely advertised and checkable online.
We then checked the breeding plans listed on the websites and Facebook pages of those kennels and contacted perhaps 6 or 7 of them. Some were not interested in us as they were looking for high level competition homes, some had no plans to breed or massive waiting lists etc.
One of the kennels however mentioned that a bitch they had sold as a puppy had been very successful at gundog trials and the owner was planning to breed her to continue the bloodline for herself. We got in touch with her and did the same checks on health etc, were interrogated by the owner and joined her puppy list.
So, actually, even if you don't want a particularly high end show dog, contacting breeders you are interested in can be a good starting point. This is not so likely to work with the minefield of cross bred dog for the many reasons previous posters have outlined. I don't think I'd even try to find a good breeder ( and by good I mean fully responsible, not kennel club) of a popular cross these days.