Would be MUCH better to just send me the mainspring itself in one of those padded envelopes. Couldn't cost much. Other than appearance, the broke mainspring is not much good now. If I can match it very close with one of my parts locks, job done. I'll just mail both springs back to you.
If I can't get a close enough match, I'll send the spring to Jeff Miller or Earl Kathan and have them forge an identical spring. While this could be done with exact measurements and photos, it would be so much easier and faster to have the actual piece at hand.
One way or another, you'll end up with a working spring. But I'm betting I have one that will work.
Rick