If you really can't find a replacement, might it be an option to 3D print the parts and use a hex mounting instead of a spline system?
There are surprisingly strong materials that might be strong enough (though it would be practical to add a little flesh just to be safe), and looking at the size of the part it wouldn't cost a fortune either.
PS: Also, could it be worth looking into the 22-4's steering bellcranks despite the fact there might be fit issues with metric parts on non-metric car...