You should either buy a new/used pod containing that, or have a machinist make one for you, or check-out some lesser Honda of similar vintage, as the button is probably identical.
Around this time I remembered that I had some 3/8" Al rod left over from another project. And that Al machines so easy I could probably chuck it in the drill press and file it down to what I needed. So here is the prototype before I shortened the rod:
Once I roughly filed down the piece I moved to a finer file, then 600 grit, then 1500 grit, and then Semi-chrome on a paper towel. And here is the final switch back in place:
So now my starter switch is made from billet Aluminum. And yes it works, and even better the starter does as well.