Looking for "recessed" seatpost bolt

The very old seatpost binder bolt on my Colnago MXL snapped yesterday
while changing the seatpost. The tabs that take the bolt halves have a
recess cut into them that is just a bit too small for the Campy binder
I had laying around. That bolt will clamp but I'm thinking it won't
load properly because the outer surfaces of the clamp ears taper to
the rear of the lug, while the floor of the recesses are parallel to
each other. Anyone have one of these frames and/or knows of a binder
bolt with narrower heads than this Campy bolt?

thanks,

tf