Help- Need a 10mm Seat Post Binder Bolt

[Rsborno]

I need a seat post bolt and nut for a 20yr old Casati frame. The head of the bolt and nut must be
10mm round to fit in the frame recess. Standard Campy bolts and others I've tried are too big in
diameter to fit.I have tried many local shops and on line places with no luck.Current Casati
importer doesn't have them. Thanks for any help. Richard