Reputable breeders will not guarantee weight, so if weight is important to you - you may want to but an older yorkie (at least 6 months of age). There are many people that will tell you a weight to sell a pup. But a repuatable breeder will not guarantee weight and would on be a guess. You cannot go by the weight only of the parents, but also must look at it lines - grandparents and etc.. The above mention of adopting a rescue is a great idea too.
There are a lot of backyard breeders and millers here in Georgia, so be very careful. You want to make sure the breeder you go with have their pups and dogs health tested and evaluated by experts. That they do not have pups all the time and will ask you a lot of guestions and check your references before placing a pup in your home.
Shampoo - no shampoo can alter a coat. Either they have a good silky coat or they do not. This is genetics. A shampoo or conditioner can help, but not alter a coat texture.
Your best bet to find a good reputable breeder is to come to the upcoming AKC show in Atlanta at the Expo Center the weekend of August 25 - 28th:
http://www.onofrio.com/plist/grif2pl.pdf There will be some top breeders there (some have won at Westminster) and many are ytca members. It will be a great chance too - to see some very nice AKC yorkies! I will be there too showing one of my champions, but I do not have any pups. It will also give you a chance to talk to some other breeders.
Best of luck in your search.