There are a lot of vendors selling silver product. Remember in México, silver is thought to be cheap and only for tourists. You will find a lot of silver products at this location. Also, you will find obsidian rocks for sale. Some of these types of things will be just a round stone, or something more elaborate like a statue. Also, there will be salesmen everywhere with Aztec flutes.
Around the inside perimiter of the site you will find several shops that not only sell, but also manufacture obsidian art and other stone objects for sale. Shop and compare quality and prices before buying.