Campy rear axles from this period are 10m x 26 TPI with 55 deg thread angle. This is a thread size that is about as obscure as it gets. Not a chance of finding a die this size. Even it you found one the a new axle would be much less money. I would take the cone and lock nut off of the other side so you can remove the axle from the hub. Hold the axle on the untreaded center portion, soft jaws in a vice for instance. Unscrew the cone, it's made from hardened bearing steel so it will force the soft damaged axle thread back into shape. Worst case, you need a new axle and cone. If you want to avoid the chance of ruining the cone, just cut the damaged thread off of the axle with a hack saw and file the end smooth. In this case you will need another axle. Jim Merz