The Jew’s harp is very widely used; in fact, according to History of the Jew’s Harp, the two continents where it was not indigenous were Africa and Australia. There is a long history of the Jew’s harp being used in the British Isles (The Jews-Harp in Britain and Ireland (SOAS Musicology Series): Michael Wright: 9781472414137: Amazon.com: Books); and inasmuch as Australian folk music is based on Anglo–Celtic music, that’s enough to explain its presence there.