I don't want to sound sarcastic or anything but why is such a small size soooo important to you? I would be worried about the health of such a small dog.
When I was researching breeders in my area my main concern was getting the puppy from a reputable breeder that had references and was recommended by the YTCA.
The breeder told me Brutus might be about 6 or 7 lbs but to tell you the truth I wouldn't care if he went into the Guinness book of World Records for being the biggest Yorkie as long as he's happy and healthy!