You can get diced Hatch green chiles online here! Pick the heat level you prefer.
You could also make this in any shape or size baking dish, including as muffins, however your baking time will vary. You will know it is done when a toothpick inserted in the center comes out clean or with crumbs.
If you do not have buttermilk on hand, simply add 1 Tablespoon of fresh lemon juice to 1 cup of milk and let it sit for 5 minutes.