Buying a puppy should be a well thought decision, since a dog needs attention and availability of the Owner. The choice of race and the Breeder is the most important aspects of this decision. Before choosing a race, look for basic information about the temperament and care of the breeds that interest you.
The Yorkshire Terrier is 3rd race with the largest number of dogs registered with the Portuguese Kennel Club. Unfortunately this large number of records in Portugal does not mean quality. Most Yorkshire in Portugal are outside the standard of the race due to poor quality of the dogs used to breed. The breed standard is the description of morphological and behavioral characteristics of each race, provide guidance to judges in the show ring and serious breeders.
If you want to buy a genuine Yorkshire, study the breed and ask for guarantees to the Breeder. Dogs with LOP are not synonymous with being "true" Yorkshire, it just means that parents have pedigree (3 generations recorded in the Book of Origins Portuguese). There are many small dogs in kennels to adopt, if they have availability to get a good Yorkshire, adopt one.
In Portugal you can find some good breeders with dogs, validated in shows, choose a puppy from one of these breeders. Contribute to the dignity of the race.