Buy a set from a modern sport bike if you don't mind the looks. Or buy the linkage from a modern bike. The spline is the same, and I'm sure you could make it work with a few dollars at home depot and some quick thinking.
The rearsets I have, from a gsxr750, has an aluminum rod, and it's a lot stronger then the threaded rod you can buy at home depot or lowes.
Others will be envious of your sturdy rod