I know NWSL makes a quartering jig for HO scale. I don't know if they do one for O also, I have never see one. I think some of the custom machinests have made their own.
Until recently, most 3 rail locomotives were not very good models, so modelrs interested in getting scale locos were not interested in converting them. That has changed a lot. However, many of the ones done in 3 rail have also been done in 2 rail.