Fish bones are available in any oriental market that sells live and fresh fish. The bones that are left over from filleting fish are packaged and sold separately. Fish heads may be included among the fish bones. I recently purchased a package of Garupa/Grouper fish bones which was used in this recipe. Marinating the fish bones in garlic paste, turmeric and salt removes the fishy smell.
The green chilies are of a tiny Thai variety that I grew in a container on my front porch. When the weather got too cold I had to harvest the remaining chilies on the plant so I froze them in a ziploc bag and have been using them ever since. If left to ripen on the plant, the chilies turn a bright red.
Chayote squash may be replaced with Lau/Lauki (Bottle Gourd) or Zucchini.