And they are readily available. For instance, I live in the sticks (the boonies). I complain all the time about living in the middle of nowhere, but I find these at a grocery store nearby. Chances are you can find them too. Size wise, they are about the length of a bell pepper, but they are darker and more triangular.
These chiles are most widely known to be the pepper used in the dish Chiles Rellenos (stuffed chiles). They are also used in rice dishes and casseroles such as my Pollo en Pipián Verde. They are somewhat hot, but not like a jalapeño or serrano chile.
I don't think I've ever used them in a recipe that didn't call for roasting and peeling them. The roasting deepens the flavor and makes removing the peel super-easy. Here's how to do it.
When roasting their poblanos, some people use their oven or even just the flame of their stove top. I think the toaster oven is easiest. I just put them in there on the highest setting. It took about 8-10 minutes per side today to roast a few poblanos in my toaster oven.
You'll know when a side is ready because the skin will be bubbly (big bubbles) and should be blackening on those bubbles. When the peppers reach that stage, just flip them over and do the same thing on the other side. In the picture below, the one lying across in the front is ready to flip. The others are not.
Then you let them sit till they are cool enough to handle. I took pictures of mine while I waited:
When they are cool enough to touch, just pinch a bit of skin and begin to pull: