Maybe 3-5lb would be more realistic...And that's still tiny. I don't know of any reputable breeder that would intentionally breed for a 2lb dog.
Go to
www.ytca.org and try to find a breeder that may just happen to have a smaller one. Smaller ones are kept longer by breeders, so it's possible that they may have a 6 month or more yorkie.
Good luck! And I hope you reconsider the 2lb idea...Even if you get a healthy one, vet visits will be much higher because the vet will need to take extra precautions that are not necessarily done for a 5-7lb yorkie.