There are 3 classes of medical we mainly deal with.
Class 1- required for commercial pilots. (valid for 12 months)
Class 2- Most common. Required for PPL and RPL.
Both of these medicals must be issued by a DAME (Designated Aviation Medical Examiner)
https://pilotmedicalsaustralia.com.au/ will put you in touch with Dr John who makes a monthly trip to Moruya to conduct medicals at Merit Aviation.
Basic Class 2- Can be issued by a wider range of doctors, but does have limitations such as day VFR below 10,000ft with a maximum of 5 passengers.
https://www.casa.gov.au/licences-and-certificates/aviation-medicals-and-certificates/classes-medical-certificate for more information from CASA. (Note there will be questions on this in your exam, so you must know about validity and type of each class)