Campagnolo track nuts are £21 EACH and nothing else will fit. You'd think someone else in the world would make a 10mm x 26tpi nut, but no. Even the Germans only have FG 9,5 and FG 10,5 - not FG 10,0 (which would probably be the same).
If I ever have to buy new ones, I'm only using a 6-point spanner on them!