For a short while in 1977 only, a full Campagnolo Grouppo came with a quite frame rare accessory, to make it street-legal in the USA :
http://www.ece.ubc.ca/
This part was only part of a full grouppo purchase, straight from
Campagnolo, in a boxed grouppo-set. If you bought parts from a
typical american supplier (such as Bike Warehouse or Turin Cyclery
Co-Op), they got their stuff through the bike maker after-market and
this part was not included. These were only available on full
grouppos purchased through the Ochsner USA distributor in 1977 !!!
http://www.ochsnerusa-store.com/
I'd say that this has to be the rarest campagnolo part, hands down! It's the only one I've ever seen !!
- Don :-) Gillies
San Diego, CA, USA