As an example NSW RMS release the following data sets on a quarterly basis for vehicles registered in NSW. Of interest in particular in the data sets
1 Motive power by vehicle type (http://www.rms.nsw.gov.au/about/corporate-publications/statistics/registrationandlicensing/tables/table114_2014q1.html ) which breaks down the registered vehicles by type and fuel.
2 New registrations by fuel type and vehicle type (http://www.rms.nsw.gov.au/publicationsstatisticsforms/statistics/registrationandlicensing/tables/table126_2014.html )
Request – Motive power by vehicle type and new registration by fuel type and vehicle type statistics nationally on a monthly or quarterly basis