Hi and welcome to YT. One great way to look for a reputable breeder is through the Yorkshire Terrier club of America breeders link.
Yorkshire Terrier Dog Breeders- Yorkie Puppies
Also in the YT library there are many articles to help find a GOOD breeder. here is one, check out the other articles for great information.
http://www.yorkietalk.com/forums/bre...e-breeder.html
It is very important to find a good breeder and do your research. I say this from experience as I did not. Buster I later found out is from a commercial breeder most likely a puppy mill. When I first brought him home he was very ill and I spent thousands of dollars just to keep him alive. In the past few years I have spent thousands more due to the fact that there was no testing and he has many of the issues that go along with a bad breeder. A good breeder screens out these genetic defects by not breeding a dog that carries these genes. Issues may come up with a dog who has been responsibly bred yes but you are at much more of a risk with irresponsible breeders. Good luck with your research Yorkies are wonderful companions.