Campagnolo did not typically include freewheels in it grouppos. The only campy FW I have ever encounted were uber expensive race only FW with aluminum cogs that wear out in very short time. Italian, british and ISO standards all share the same 24TPI thread pitch so you wouldnt be cross threading anything, only difference is several thousands inch difference in the diameter of the threads, not a big deal to interchange.
http://sheldonbrown.com/freewheels.html
Note that ISO FW thread diameter is inbetween British and Italian so would be the better than british if you are trying to source a new hub for an Itialian FW.
If you are bothering to replace the hub, you might also want to upgrade to a 7-speed FW which works fine with 126mm spacing. Also, rather than replacing the hub, you likely could just replace the bearings, cones, races, axel as needed; unless of course the spoke flange is broken. The cones and races can likely be scavanged from another hub if needed, they probably are identical deminsions with campy hubs.