I can't help with breeders, I have not heard of people specifically breed for dwarfs anywhere. I am curious why you are interested in a chin with dwarfism? I'm not sure how much research you've done, but they can be prone to health issues and that can lead to a shorted life span. It's a recessive mutation, so to intentionally get them specifically you would likely be dealing with a lot of inbreeding. Inbreeding can cause issue itself, but when you have an animal that is already prone to health issues it's not a good idea to breed it to another that is prone to the same issues. They do happen from time to time in breeding, but I don't think it's a good idea to be intentionally breeding for them. Dwarfs, when they happen, are normally removed from breeding.
My first chin was a dwarf (we didn't know when we bought her, we got her at a pet store), she had seizures and only live a few years, chins normally live 15-20 years.