Good luck finding one at a reasonable price and be careful using the word teacup here, because there is no such thing.
There are tiny ones and small ones. Try to specify the size you want your pup to stay when it reaches adulthood. Yorkies can be 2 to 7lbs and over. You may want to read up on yorkies online. Your wife will have to take extra care with the tiny ones as they are fragile. They can get stepped on, won't eat and bones break easy, etc. This is not saying they can't be healthy, there are some very informative breeders on here. Once you get your new puppy, make sure she introduces her new puppy on here. She can use your name, there is a lot of good information and advice given her. So research before buying, and try to check all breeders out and get references if possible. I think a yorkie would make a really nice V-Day present. If you want to talk private to a breeder or someone selling their pups, you can send them a private message. Good luck