i try...
sometimes the task isn't as easy as i think it is.
i have no idea what you tried with your searches, but...i typed in a whole crap lot of stuff.
stormy ocean wallpapers
ocean storm wallpapers
stormy seas wallpapers
rough seas wallpapers
anyway i could phrase it, i tried. if you can think of more, you might turn up more. or perhaps someone else can do it better than either of us can. or the pictures just don't exist on the net yet.