Hi Steve
Had same problem with mine.
When I got my wheels had to buy a full set of wheel nuts, paid six quid a peice for the nuts. Nuts fitted OK and could just about get my Halfords wheel brace (bar type with sockets ) to fit.
Nuts loosened in no time so had to buy a thin walled socket from Halfords with breaker bar to suit which solved problem.
I do believe however that correct size nuts are available but my local dealer could not get hold of them.