Have you checked the Yorkshire Terrier Club of America's breeder referrals? That's the first place I look at when searching for a breeder:
http://www.ytca.org/breeder3.html#IA

There are only seven, so that should narrow it down a bit. As usual, go through the normal questions: health testing, champions, active participation in agility and conformation and similar sports, etc. etc. That should help you narrow it down to the "one" breeder