Here's the breeder list for NY from the national website for the breed: http://www.ackcsc.org/index.php/breeder-referral/51-ny
We have not owned a Cavalier King Charles Spaniel ourselves (but our neighbors have one and they are SO darned cute!), but having been in the dog show world with our Boxers, I do know how to find a reputable breeder. Go visit the breeders. Observe how they keep their dogs. Do the dogs look healthy? Do they interact well with humans? Ask what kind of health problems they have experienced with their dogs (and if they tell you their dogs have never had problems - RUN the other way - all breeds have some health problems, and responsible breeders breed AWAY from those problems to improve the breed). Bring your children (if possible) so you can see how the dogs react around children. You should be able to meet the dam (mother dog), and maybe even the sire (if he belongs to the same breeder - they don't always).
Be aware that if you buy a show-quality puppy, it is fairly typical that the breeder will ask you to sign a contract promising to show the dog until s/he "finishes" - that is, to show them until they have obtained enough show points to qualify as a champion dog. This also means you can't have the dog spayed/neutered until they "finish," which can be problematic (I speak from experience). If you don't want to show the dog, then you can ask for a pet quality dog rather than a show quality dog. Puppies that don't qualify to show might have a slightly different color or pattern than would be allowed, or they are slightly too small or too large - nothing that would matter to you, just that the dog couldn't be a show dog. Ask about breed-specific quirks - how easy are they to train? (You may have read about this already - but listen to what the breeder has to say, too.)
The breeder should show an interest in you, and should ask you a lot of questions. If the breeder shows no interest in you, be concerned. Good breeders feel very strongly about finding good homes for their puppies, not just ANY home for their puppies. Every reputable breeder I've ever met has been willing to talk my ear off about their dogs, and the breed in general.
Good luck in your search!