Hey I did a quick search here is what I found:
— Pennsylvania Yorkie Rescue — ADOPTIONS —*RescueMe.Org <--- This one only has a mix right now but you might want to check back
http://yorkie.rescueshelter.com/Pennsylvania <-- This one has a directory of a few different organizations
Animal Browse <-- a Few purebreds on this one that it looks like are in PA
Hope this helps! Good Luck!