I think it's so sweet you want to give your grandparents another yorkie. Instead of surprising her with a puppy, I think it would be better to let her pick out the puppy with you.
I suggest going to the YTCA's website and looking at their breeders
http://www.ytca.org/breeder4.html
There is one listed in Arkansas. I don't know anything about her but its worth looking into.
Northshire
Dorothy Naegele
Cabot, AR
72023-3660
(501) 843-9843
northshire@futura.net
There are also several listed in Texas, Louisiana, and Oklahoma.
__________________
~Magnifique Yorkies~
Purchasing from backyard breeders, pet shops, and puppymills perpetuates the suffering of other dogs.
Educate yourself and buy from reputable breeders or rescue.