What about calling a local yorkie rescue? They may have some other means to help rescue the poor little guy.
Have you talked directly to the manager of the pet store? Let them know the sick puppy could infect the rest of the puppies and they could all get sick..
I don't know if they will care or not, unfortunately a lot of times the sick animals are put to sleep rather then receiving medical care because it is less expensive.
TG, in Nevada there are not any pet stores that sell dogs or cats. It is illegal, as it should be everywhere!