Are breeders registered with breed clubs reputable or am i now only looking at Cruft winning dogs when all I want is a family pet?
The vast majority of show dogs, even those who make it to Crufts, are primarily family pets and a fair proportion of show bred puppies never set foot in a show ring. You don't need to avoid breeders who show to a high level because you're not interested in doing it yourself. My three whippets have got numerous champions in the pedigrees, including a Crufts Best in Show winner, and they're absolutely fabulous pets 
I see a breeder showing as a positive thing (even if I'm not looking for a show dog) for two main reasons. One is that it shows at least some desire to have their dogs independently evaluated, rather than breeding from them just because the think they're lovely. The other is that shows, especially larger ones, are actually a pretty good test of temperament. The dogs need to be happy being examined up close by complete strangers, they need to be happy around large numbers of people, lots of other dogs (of all shapes and sizes), loudspeakers, sudden bursts of applause, flappy marquees, all sorts. Particularly in my breed where there can be a tendency towards timidity if not enough concern is given to temperament I find it a very good sign if both parents are successful show dogs.
Of course showing isn't a guarantee of a good breeder but I would always expect any good breeder to be having their dogs independently evaluated in some way or other. Whether it's through showing, working, dog sports, PaT qualifications, etc.
I agree with getting in touch with your regional breed club, they should be able to help put you in touch with decent breeders who are planning litters. I'm with Whitney that it's better to find a breeder rather than look for a litter already on the ground. Champdogs have a good little guide to buying a puppy and their list of questions to ask a breeder is also well reading and keeping in mind.
With regards to health testing both parents should have a current BVA eye test (repeated annually) and a current BVA gonioscopy (repeated every three years). In an ideal world they'd have both been hip scored with results lower than the breed average as well but it seems very few breeders hip score in cockers. Both should have had DNA tests for (or be clear by parentage of) adult onset neuropathy, exercise induced collapse, macrothrombocytopenia, familial nephropathy and prcd-PRA.
Whilst I can understand the argument against hip scoring if dysplasia isn't a major issue within the breed as the test usually involves the dog having a GA, I absolutely would not compromise on either of the eye tests or the DNA tests.
I'd also look for a breeder who is paying attention to the inbreeding coefficients of their matings. Closed gene pools inevitably lead to a reduction in genetic diversity and breeders should be doing everything they can to preserve what genetic diversity there as much as possible. This is a really good article about COIs and why they're so important.
You can use the Lennel Club Mate Select tool to find out health test results for individual dogs and also check the COIs of a specific dog or mating.