Place the carrots, potatoes, onion, celery, and bouillon cubes in a stock pot; pour enough water over the vegetables to cover. Turn heat to medium-high and bring to a boil; allow to boil for 30 minutes. Add the oysters with their juices and 1 teaspoon black pepper; boil another 3 minutes; reduce heat to low. Stir in the evaporated milk and butter; cook and stir until the butter melts completely. Season with salt and pepper to serve.