Can I download the Quicken for iMAC from Australia?

Correct...Quicken is only developed and supported for those markets. That said, as long as you do not want to download data from non-US and non-CA FIs/Banks directly, you can still use these products. You can set your base currency to AUD.

You may also want to read the following to purchase and use Quicken outside the US and Canada (there are potential work-arounds; read the thread to the end for additional resources and tips)