Just have someone open M4 fire from the boat, will be a worse but at least somewhat adequate substitute (the Minigun would be too OP). The actual thing is impossible to add since the weapon is just a part of the boat model, and barely any mod can add any sort of weaponized vehicle into the game, let alone a SA-MP script. Even if we were to add a hypothetical mod in, that would require us to switch to 0.3DL and y'all would have to update your clients, and new 0.3.7 players wouldn't be able to join.