I broke that bolt of on my old 86 half ton. I was getting rid of it anyway, so I scribed a note
on the diff. cover that said it broke off and something like "sorry" or "good luck".
This is a highly impractical solution for what might be a fairly easy part to find in your case, but I had a bolt electrically disintegrated out of a dirtbike chassis one time. The guy was a specialist around here, but there might be someone around you. Ask machine shops for a reference. It's impractical because it cost me 200 bucks, but a new bike frame was around 500.
