Puya chiles are quite similar in appearance (but smaller) and flavor as the guajillo but with a more intense heat. The puya can be used with guajillo to make the dish more "piquant". You can also mix the puya with other mild chiles like New Mexico for a richer, hotter sauce.
Puya are typically found in Mexican markets and less so in larger local grocery stores. You can also buy puya chiles online in our store at Gourmetsleuth.com