What is a substitute for Poblano Peppers? I have a recipe that calls for Poblano peppers but our store does not have them. I found this which references using Anaheim Peppers but they don't have those either.

What is a good alternative?

It is a roasted stuffed pepper dish that I need them for.
You can stuff any pepper which is large enough.

Poblano are moderately spicy.  You can use bell peppers, but they will not be spicy.  You might want to make up for that by including some spicier small peppers in your stuffing, perhaps a serrano or a jalapeno or seventeen, depending on your personal taste.