ForYourInformation:
Here are two enquiry screens on the NSW RTA site, that you may find useful.

"FreeRegistrationCheck"
https://myrta.com/regcheck/pages/content/enterVehicleDetails.jsf 

"VehicleHistoryCheck"(Costs $18)
http://www.rta.nsw.gov.au/myrta/rego/vehicle-history-check.html 

The RegoCheck tells you:
On the first screen....If the plate is being used or not, the Year, Colour, Model, Vehicle Type and last x4 digits of the Chassis Number.
I found this to be a bit flakey.ie, previous plate and current plate for the same vehicle, gave the same info...infers that the previous plate is still valid.
The "plate used or not" can help to find a possible availability of a plate - I found x2 that I am interested in.
The second screen adds the Tare and/or GVM weights, If Rego is current and expiry date and any concessions, also CTP expiry date and provider.

I presume that the availability of this info compliments the dropping of RegoStickers in January??

'Didn't try the History enquiry.......erm...$18.