Take the seat lock/barrel or the helmet lock out (very easy to do) and take it to a proper locksmiths who do car key cutting and they'll cut you a key to fit using the barrel.
The ignition has one more leaf than the other two but if the locksmith has the right programme on his equipment it'll know which one to cut.
Or at the worst there will be a two or three key option, in which case just have a key cut off each as they're cheap enough (about £4 each) rather than going back and forth to the key shop two or three times having another notch cut until it fits., .