I think left-hand helicoils are used for bicycle pedals when the thread strips from aluminium cranks, so bicycle repairers may have that one specific size.

Here is a source for left hand helicoil kits, both inch and metric:
http://www.newmantools.com/sti/stilh.htm#metric
I haven't done business with them, but you might give them a try.

For future reference, the iterative, washer-at-a-time pulling method you used is always hard on the threads involved because you never have a full thread engaged. When one of the parts is aluminium, it is just not the best way to do the pulling job. Provided you pull the lower bearing out with the shaft, and separate them afterward, you could probably use Tanaka's recommended method for removing the lower bearing from the aluminium adapter:
[Linked Image]

Note that the wooden block must have a large enough hole in it for the shaft and bearing to pass through. This method would work most easily if you removed the bevel pinion beforehand, so the upper output shaft bearings could drop out along with the output shaft and its lower bearing. I note you did not remove the pinion because of difficulty removing the circlip.