In the past I have found some used hand cranks at the restore. If you are fortunate you might find some good used ones. Most of these old style cranking mechanisms were notorious for stripping and breaking. The greatest problem was that the wooden windows had a tendency to swell a bit and not close easily. As a result most people force the crank to try to open and close the window. Of course this breaks the cranks. The best option is to never force the cranks. In the fall have someone on a ladder outside push on the window to help close it properly. Taking a few precautions will save the cranks. The last I checked there were replacement cranks available for about $90.00 each.