I would just solder a gold plated key contact wire in place of the broke contact wire, because I do not have a spot wielder that was used back then. But gold is softer and you will not get the million cycles out of it that was wanted back in the day with both the bus rod and the contact cross connecting.
Many in this group probably have a contact of this type or similar in their junk draw that you might salvage the actual wire from. I will keep an eye open. They once were common spare parts.