Heat 1 tablespoon butter in a large skillet over medium-high heat. Stir in the mushrooms, and cook until golden. With a slotted spoon, remove mushrooms, and set aside.
Melt remaining 1 tablespoon butter in the skillet, and stir in shrimp and scallops; cook, turning, until the shrimp are pink, about 3 minutes. With a slotted spoon, remove shrimp and scallops, and set aside.
In a medium bowl, mix together the flour, black pepper, and clam juice.
Pour clam juice mixture into the skillet, and bring to a boil. Reduce heat to medium-low, and simmer until mixture thickens. Reduce heat to low, and stir in sour cream. Return mushrooms, shrimp, and scallops to the skillet; mix in sherry, and cook to heat through. Sprinkle with parsley.