I really encourage you to check out rescues first. Because Yorkies are so popular in pet stores and such, there is usually a large number of Yorkies in rescue.
Yorkshire Terrier Rescue Network, Inc.
Dr. Dale A Heisler, DVM
2311 Freeway Dr.
Reidsville, NC 27320
(336)349-4918 fax: (336)349-7639
[email protected]
http://www.yorkshireterrierrescue.net

United Yorkie Rescue Inc (serves all states)
http://www.yorkierescue.org
But if you do decide to go to a breeder, be absolutely sure you're going to a breeder who's breeding ethically. It's not enough to bring their dogs to the vet every year for check-ups. They MUST health test their dogs via OFA (Orthopedic Foundation for Animals) and CERF (Canine Eye Registration Foundation). In fact, those two tests are now required by the Yorkshire Terrier Club of America. If you find a breeder you like, demand to see the dogs' test results of PRA (progressive retinal atrophy), luxating patellas, thyroid, and perhaps Legg-Calve-Perthes. If the breeder hasn't even heard of these tests or assures you they've never had these diseases appear in their stock, run the other way. They're simply trying to sell you a product, but you're looking for a responsibly bred puppy. It may take awhile, but it is worth it.