A data visualization of Koala Hospital data has been published on the Datavis website. The dataset, which is here, contains approximately 40,000 rows of data captured from 1996 to 2017.
The "Koala Local Government Authority - stacked graph" shows a serious and disturbing decline from 2010.
Koalas were most likely to make their way to the Koala Hospital during the months of August to November. Presumably this is due to their migratory nature during these months.
You'll find more information here.