Hi, sorry I got it wrong. I've been doing stuff with various M10 thread forms and got confused.
Looks like:
Shimano is M5 x 0.8,
Campag is M5 x 0.5.
I'm afraid I can't help you with where to get one in the UK. Might be worth a troll though roadie bike shops and see if they would have any knocking about.
I've had a look and I don't have a M5 x 0.5 die, otherwise I could have made you one. I've been making Shimano ones recently. Dies are pricy as well, particularly if you just need the one adjuster.
I'm off for a week, but I'll have a look for a die when I'm back to work, but its an uncommon size for my line of work, so unlikely. I'll look anyway.