If you can't find Anaheim chilies, you can substitute them with Poblano, New Mexico green chili, or even roasted red bell pepper. Just be aware that the flavor will be different. Anaheim chilies tend to be milder, so if you use a hotter chili like a New Mexico, your dish might be spicier than intended. If you want to stay closer to the original flavor, go for a Poblano chili.