Where to get the quartz crystals:

You can find quartz crystals in your local new age or crystal shop, Amazon, Ebay or Etsy.

When I used to buy crystals for resale I got them from this guy.

The purchase process is a little old-fashioned (no shopping cart on the site) but he is reliable and he mines the crystals himself. 

https://arcrystalmine.com/crystals_results.php?category=1