I think that's the Blitz high output lamp have you tried a LightForce dealer in Sydney? Just guessing their probably expensive through them like here in the US around $18.00 US plus postage.
BulbConnection has them for $5.75 plus postage, it looks like they ship to Australia...worth a try.
You might want to try sourcing from a Australian company that sells dance floor lighting and DJ supplies. Bi-pin 100 watt-12 volt bulbs are very commonly used in nightclub lighting fixtures.
Here's a list of over 150 companies. I'd be surprised if you couldn't find what you need from one of them.