How-To/Mechanics: Old stems?

Man, I busted the stem bolt on this old Mercier I'm bringing back to life.
The folks at my bike store told me that the old French bikes all did their own thing with hardware, so I'm pretty much boned as far as getting a new bolt.

I'm looking for suggestions. I heard that people have been able to jam a Japanese quill into an old French headset, but I don't even know where to start with that.

Any ideas?

ebay is the way to go. if they dont have one listed right now check back in a couple of days. one will show up.