Do you mean that the three pins have broken off? If so the dealer is probably your best bet, but I dont know what codes you would need in order to get one......or whether all the locking wheel nut keys are actually the same. If it turns out they are all the same when I wanted to order a new key this was about ?25, but for a whole new set of locking wheel nuts and key this was about ?13.
Alternatively a drill will do the same job, or so I am told one of those 'gator-grip' sockets can undo some wheel nuts.