Where to catch wailord?

You cannot catch a wailord, but you can catch a wailmer from Routes 103, 105, 106, 107, 108, 109, 110, 115, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133 & 134, Dewford Town, EverGrande City, Lilycove City, Mossdeep City, Pacifidlog Town, Seafloor Cavern, Shoal Cave, and Slateport City (Fish). They are common. Then you can train the wailmerinto a wailord.