If there are several breeds of dogs, chances are the breeder cannot devote the time it takes to become really knowledgeable about the breed. If there is more than one litter at a time, it is very difficult to give the puppies the attention they need and may indicate that the primary purpose for breeding is profit, rather than a sincere desire to sustain and improve the breed. Keep in mind that you are entering into a decade long relationship. It's worth the effort. If you answered yes to every one of these questions, you're ready to start contacting breeders.
Responsible breeders can have waiting lists from a few months to several years.
Rescue dogs may or may not have been bred responsibly. However, adult rescues can be evaluated for signs of a problem before you fall in love, which can't be done with a puppy.