It's pronounced the same as the car manufacturor,
Kia.
It's NOT an Australian name, though! It's widely used throughout the English-speaking world. A Google image search for Kiah gets 5260 hits worldwide; if you restrict the search to Australian sites, you only get 217 hits.
There are only a very small number of truly Australian names, and this isn't one of them.
♦ Chrisell ♦
All we have to decide is what to do with the time that is given us. - J.R.R. Tolkien.