I encounter left handed bolts all the time.
On my left grinding wheel, on my circular saw arbor, on my stick edger (I've heard of left handed lug nuts, but never seen them first hand), left bicycle pedals, turnbuckle locking nuts, etc.
Never have I needed to torque one though. The idea behind left handed bolts is that they're used on rotating parts in ways that make them self tightening (where a right handed bolt would be self loosening). In such a use, all you need to do is get it snug, and leave it alone. I have never encountered a torque to yield, or torque critical left handed bolt. Is this something that comes up in aerospace use perhaps (for holding on counter rotating props)?
Oh, and there are those left handed thread CGA gas fittings (like for propane) where the threading is chosen to prevent hooking up the wrong thing, but again, not something you'd put a torque wrench on.