The best way to find a Havanese breeder is to go through the breeder directories of organizations such as the American Kennel Club or the Havanese Club of America. Local kennel clubs are also a good option to find breeders in your area.
Membership with a kennel club does not guarantee that a breeder is responsible and ethical, so you need to do more research after finding potential breeders. One of the first things to ask about is genetic health issues. Havanese dogs are prone to multiple serious genetic health conditions, including eye diseases, skeletal issues, joint issues and liver shunts. A good breeder tests her parent dogs for these conditions before breeding and is happy to show test results and answer all questions.
Responsible breeders also welcome visits to their facilities. When you visit, the dogs should be healthy and the facilities should be clean. The breeder should know each dog personally, and the dogs should be happy to be handled. Good breeders generally show their dogs and only breed top dogs to other top dogs, and they should be able to explain why they chose to breed a given pairing.
Responsible breeders should also be interested in you. They should interview you to make sure you understand what taking care of a Havanese entails, and to make sure you're capable of doing it. They should provide reasonable health guarantees for their puppies and be willing to take back adult dogs if you cannot care for them anymore.