Warning, complete speculation ahead:
The article quotes 261 Tesla's in NSW when we know that there were 210 registered as at September 30 according to RMS. Perhaps they have a deep source in RMS and can get updated figures more frequently but they're not saying.
Based on the articles figures, NSW has 261/536 or 48.7% of registered Tesla's in Australia.
So if sales continue at 60 per quarter in NSW and the same rate everywhere else that makes NSW registrations 270 on Dec 31 * (100/48.7) = 554 Teslas Australia wide by years end.