Heat a medium-size cast-iron skillet over medium-high, and add chiles. Press flat using the back of a spatula, and toast until slightly softened and a shade darker, about 30 seconds per side. Remove chiles from skillet, and let cool slightly. Wearing gloves, if possible, trim stems of chiles; cut chiles open, and remove and discard seeds. Cut chiles into small pieces. Place chile pieces in a small bowl, and add boiling water to cover. Let soak until soft and rehydrated, about 15 minutes. Pour through a fine wire-mesh strainer into a bowl; discard liquid.

Transfer rehydrated chiles to a blender; add garlic, oregano, cumin, and 1/2 cup of the chicken stock; process until smooth, about 1 minute. Set aside.

Heat 1 tablespoon oil in a large Dutch oven over high until smoking. Sprinkle pork evenly with salt and pepper. Add half of pork to Dutch oven; cook, turning occasionally, until browned on all sides, about 10 minutes. Transfer pork to a plate, and set aside. Repeat process with remaining 1 tablespoon oil and pork.

Add onion to Dutch oven, and cook, stirring often, until softened and beginning to brown, about 8 minutes. Add reserved chile mixture; cook, stirring constantly, until fragrant, about 1 minute.

Return pork and any accumulated juices to Dutch oven; add bay leaf and remaining 3 1/2 cups chicken stock. Bring to a boil over medium-high. Reduce heat to maintain a simmer; cover and simmer, stirring occasionally, until pork is just tender, about 2 hours. Stir in orange juice, and cook uncovered, stirring occasionally, until meat is fork-tender and sauce is thickened, about 30 minutes. Remove from heat; remove and discard bay leaf.

Garnish with cilantro and finely chopped onion. Serve with lime wedges.