There are a few manufactures that offer "switchable mufflers."
(Not a complete list.)
However, you may just want Donkey Dlcks; as we affectionately call them here:
When you are on plane, the exhaust is wide open, just pointing down.
When you are off plane, the exhaust outlet is under the water line.
What engine do you have?
What outdrive do you have?
Do you have ITS or external hydraulic steering?
All of these play factors in what may best fit your setup.
Fred at www.trickmarine.net would be a friendly place to start.
Do a few searches here on OSO on "mufflers" and "switchable" .