According to Kenneth G Wynn in his book "A Clasp for the Few", there were some 2945 men qualified to wear the clasp, of whom 2388 came from the UK, the remaining 557 coming from the Commonwealth, Ireland.Poland, France, Belgium, Czechoslovakia, the US and Palestine. Of the contingents from overseas, New Zealand had 129 men officially in the Battle, second only in number to the Poles, and far exceeding that from any country outside of the UK .
As has been mentioned, not everyone entitled to wear the clasp were pilots. and in the case of the Kiwis 75 % were pilots, and 25% air gunners and observers.During the officially recognised sixteen-week period of the Battle, 20 of those Kiwis lost their lives and a further 40 were killed later in the war. Of the ten top-scoring pilots of the RAF, two were New Zealanders, who between them destroyed 30 German aircraft.
Wynn's book, I've just noticed, was published in 1981.