There are many, many sources.
I like to use Ebay, where there are many vendors that sell Kuchi pieces. Uberkuchi and Sirik pop to mind as two that seem to be reliable and have consistently good prices. A bit higher end is Artifacte, from Turkey. I think you may want to search for Turkoman buttons on Ebay, as well, if I understand correctly what you'd like.
In terms on non-ebay vendors, there are the "tribal trio" of vendors who have unique pieces, at reasonable prices, with good service:
Tribal Souk (
Tribal Bellydance Marketplace:: TribalSouk.com :: Tribal Belly Dance Costume Accessories)
Tribal Bazaar (
Tribal Bazaar - tribe.net)
Red Camel (
The Red Camel Home)
Each of these vendors has different things, so it is useful to check all three. I can report excellent experiences with Tribal Souk and Tribal Bazaar - beautiful pieces and impeccable customer service.