I guess one question would be, how far are you willing to travel, and do you have your own transportation? Both of my girls came from craigslist. I purchased my mutt my myself, and a zoo friend of mine purchased my newfie. My newfie was never intended to be mine, but one thing lead to another and eventually I got her.
Are you looking for a puppy or an adult dog? There are plenty of puppies on "for sale" websites like Lancaster Puppies. You should also be able to find plenty of breeders around your local area through Google business recommendations. I would watch the reviews though. Many of them in my area are suspiciously highly rated. If all the reviews are one post reviewers, then I'd assume they are paying for ratings. Also, don't be afraid to ask about spay and neuter contracts. If they question why you're against them usually an argument about "Not altering "God's" creatures" seems to stop further inquiry about it. Also, make sure he parents are on site. A basket of puppies without their parents being visible is a major red flag.
Lastly, time. Don't jump on the first dog that is for sale and seems to fit the majority of your criteria. Thoroughly weigh your options, and don't be afraid to pass up a dog you find suspicious.