Do you know the hub model (Record, Super Record, Chorus, etc) and the year it was made? Many Campy hub models share the same cone dimensions, so they're not too hard to find. Also, I believe you will find engraved on the flat outer surface of the cones some numbers which will specify a diameter (inner and/or outer, not sure if both) and a tpi (threads per inch). If it's says Campy and matches those numbers, you should be good. Also a good idea to take the axle with you to be sure the threads match.

