I would start with the breed club. Some have a breeder register for breeders that meet their standards (usually have to have appropriate health testing at the very least) others maintain waiting lists which the breeders can access.
See if the breed club has a forum and ask to join, that way you can get an idea of what different breeders and their dogs are like and it can lead to joining other groups of enthusiasts for the breed, where you will gain even more insight. You can also check on the KC site for the Inbreeding Coefficients of dogs for the breeders you are interested in.
Look for breed groups on FB, as you can glean a lot from them, eg a particular line that seems to have reoccurring health or behavioural issues.
When you start to get an idea of which breeders appeal to you, you can contact them directly for a discussion and if you are both happy, you can then ask to go on their waiting list. Some then have their own FB groups they will invite you to join, where you can get to know them and the families of their previous pups better while you wait for your pup.
Personally, I think about getting a new dog in terms of a massive commitment and responsibility, generally for 14/15 years plus, so expect it to take time to do the necessary research and find the right match for us. Some people do get lucky and find a breeder more easily, but I am cautious by nature and would rather go slow and plan in advance.
Fwiw, I know some excellent breeders who are on Champdogs, but use it as a point of contact (after which you will be vetted within an inch of your life and they expect you to do the same to them) rather than somewhere to advertise litters.