Where do you get your rear sprockets from?

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.

Ratio calculator http://www.sprocketcalculator.com/