Craigslist has basically replaced the newspaper ads for dogs. However like the newspaper ads, many adverts are for 'oops' breeds, but it is also used by unscrupulous types to take two low quality dogs, breed them and offer 'purebred' pups at half the price of what a good breeder would charge.
Rescues and breeders (both reputable and disreputable) make heavy use of facebook to promote their 'product'. There is a growing trend for backyard breeders and the like to take on the appearance of a Rescue and simply list 'adoption fee' the same as what they would have charged for the pup on a normal sale.
Finally, stupid human factor. Soccer Moms now don't want to say they the dog from the pound or an ad on craigslist, saying they got it from a 'rescue' gives them higher standing with the rest of the soccer moms same as the gluten free snacks they all buy for their kids.
My specific advice?
#1 contact AR15.com's in house dog rescue, run by joker1, tell him what you want and he will work his magic.
#2 Decide on a breed or even better group of breeds, then go on AKC and find the 'parent club' of that particular breed. Go to parent club website and there should be a list of recommended breeders. Contact these breeders. It isn't necessary to buy only from this list. Often these breeders have contacts who are producing good pups, often these breeders are helping other breeders getting started, and know when they are having litters, and can put you in contact with them.