In what sort of store might one find Teacup Yorkies for sale?

No, "Teacups" are not an actual size recognized by the registrations rather a size breeders put on them to give potential buyers a good idea that these dogs will be very small by Yorkie standards. I have found people have different ideas of what a "teacup" is so I would double the weight at 12 weeks to give you an idea of the adult size. Pet stores don't carry "teacups" because they don't weigh enough at the age they want to sell them. If you want a really small pup your best bet will be internet. I sell Yorkie's and would consider mine to be "teacup" since my girls weigh between 3-5lbs. You will pay considerably more for a "teacup" than you will a regular 6-7lb Yorkie.