Installing a dual can system on a DRZ SM would necessitate relocating the battery since it sits where the other can would go. Not that it is not possible, just can't think of any other place to stash the battery.
That said, there are pics floating around here of a converted E model that is set up for track only and it had dual cans. The head pipe dropped under the engine and the cans were angled up like on a sportbike. Looked very cool.
As for an off the shelf dual exhaust, I have never seen one.