Where Can I Find a Single Right Front Crank Arm for a Tandem?
I know that some BMXs have left side drive. I actually found this out by accidentally ordering a left hand freewheel that was backwards on my single speed!

I don't know if these cranks will work for you but it might be a place to look. Wikipedia describes left side drive here .

JensonUSA have Sugino tandem crank arms sold separately.