The breed club should be able to help point you towards some breeders planning litters as well. Like many breeds there's a national club and several regional ones as well, you can see a list of them all here. Dog shows are great for meeting breed enthusiasts as well as getting an idea of the type of dog it is you like. This is quite a good list that includes a lot of smaller shows and there's a list of championship shows (bigger, just about every KC recognised breed will be there and a great day out if you love dogs!!) here. Despite the name Yorkies are in the toy group so for shows across multiple days you need to check which day the toy group will be shown.
Also familiarise yourself with the necessary health tests for the breed. This page explains which tests should have been done on both parents. Unfortunately I don't think there are many Yorkie breeders who are doing MRIs so you may struggle to find a breeder using fully health tested dogs however the absolute minimum you should be looking for is the annual eye test plus the DNA tests for prcd-PRA and PLL. Ideally, although it's not a recognised scheme, I'd want their knees to have been checked as well. Ideally you want a COI (coefficient of inbreeding) of lower than the breed average, which for Yorkies is 9.6%. The lower the better though really. You can check the COI using this tool on the KC site providing you ave both parents' full names. You can also check health test results here.
Ideally you want to be looking for a breeder rather than looking for a puppy to buy immediately. The decent breeders will generally have full waiting lists of people who are seriously interested in the puppies before they're even born.
Expect to be thoroughly grilled by the breeder before you get anywhere near the puppies. If it's a case of the breeder handing over a puppy, no questions asked, as long as you've got the money then walk away. Expect to be asked about your house and garden, your lifestyle, your dog owning experience, what you feel you can offer a dog, why you picked that breed and why you picked that particular breeder.
They should also be happy to answer your questions and talk about why they chose to breed in the first place, why from that bitch, why they picked the stud they chose, what they were hoping for with the litter, etc.
The bitch and puppies should be kept inside and not shut away from the family. Check that they have some kind of set up like a whelping box in a pen in a well used room in the house. If there's no sign of that then the mum and pups could have just been brought in from elsewhere for you to view. Depending on the age of the litter there's all sorts the breeder should be doing to help set them up to be well adjusted adult dogs. This website gives you a breakdown of the developmental stages of puppies and gives you an idea of what the breeder should have been doing during each of them.