Much of the Campy stuff is interchangeable. I found an older design (but new in-the-box) front derailleur with a 28.6mm clamp for $2 on eBay, and swapped the clamp with that on a brand new mechanism (32mm); it required a bit of patience and technique, but I now have a brand new front mechanism with a NIB 28.6mm clamp. I think that "braze-ons" to be the ugliest of things!
- Wil
PS: an alternative is to use a shim, but IMHO it makes it look ugly (but not as ugly as a braze-on
)