To find the "correct" Campy bolt you'd probably pay more than it's really worth, as compared to the cost of a completely new seatpost, particularly from a retail source.

I would either:
1. Place a ISO/WTB in that thread, and hope a kind soul responds at a reasonable level, or if no luck
2. Go to your local industrial supply house and buy a high grade (edited) fastener.

And glad you had the presence of mind to avoid an uncomfortable end.