Nuestra Tierra offers a wide selection of jewelry that includes painstaking handcrafted replicas of classic Spratling and Aguilar designs as well as more modern designs by contemporary artists. Signed pieces include those by Sigi Pineda, Daniel Espinosa and Sergio Bustamante,
http://www.nutierra.com/products/jewelry.html and there is another site
http://www.caramba.com.mx maybe you could contact this two places and even if they don`t have what you are looking for at least they can give you advice or even tell you the right place to go, but it`s a start, I hope this helps! Good luck.
Some links that could help you when you go :
Airlines to Mexico,
Taxco Hotels,
Shopping Mexico.