If you order off marchesini or Omnia racing.com they have them and in any tooth size very good value and service.
Sidewinder sprockets do a Titanium package with a lifetime guarantee, will be on my streetbike in 13

Check the ratio chart at the bottom you might acheive the ratio you are after . These sprockets have an importer into Australia. I have a rear on atm, they are light, tough and appear well made. Where abouts in Australia are you I have a mate who owns a bike shop in western Sydney which can supply you.

I have a brand new 42T Esjot German Manufacture rear sprocket Oz $50.00 + postage, I also have a used OEM 40T which has done 4K kms $30.00 + postage, if anyone in Oz wants them send me a PM . The 42 will turn your bike into a wheely machine. http://www.sprocketcalculator.com/