Roast the peppers under an open flame on the stovetop turning with tongs ever so often to allow for even charring. This will take 3-5 minutes. Alternatively, char the peppers under a broiler until medium blackened, about 3 minutes per side. Seed and devein the peppers under cold running water. Do not remove the burnt skin.
Carnitas or roast pork are available on weekends at most Mexican grocery stores. Call in advance to check for availability.