I have been thinking for a while and come to the thought of adding National Parks and Wildlife which is in every state and territory of Australia. The purpose of the National Parks and Wildlife (NPWS) is fire response for all national and state parks/forest as well as a form of law enforcement in the form of rangers.
I would suggest a normal and large hub (stations) as everyone service. You have the choice between 2 trucks for the first truck in the hub, a heavy and ultra-light tanker, as well as a bulk water tanker, then a support unit that is the same as the support unit for the normal fire stations but this is specialized for the NPWS and its missions. From there I think its time for Dozers to be added as they are a crucial part of firefighting in Australia. They would need the same training for trucks as the US and need the crew cab semi and dozer trailer.
The NPWS can have its own calls as well as being a extra service to help for all current missions requiring tankers. Hazard reductions are a major part of preventing fires and need to be done and the NPWS does them regularly. They will have 3 types. A small, medium and large. They will have the chance to expand into bush fire missions as well.
Small hazard reduction will require 7 tankers and a support unit- 1 hub required
Medium 10 Tankers, 1 Bulk Water and 2 support unit- 2 hub required
Large 15 tankers, 3 Bulk Waters and 3 Support units- 4 hub.
Forrest fire missions for the NPWS would work brilliantly for them. With the National forest, state park POI's would grant players the ability to spawn forest fire missions which are for both NPWS and normal fire service but can be completed exclusively by the NPWS but normal fire service tankers can be used if you don't have enough NPWS tankers. The current forest fire missions will work but copy and paste but add National park to the name to differentiate them. They will need the same requirements as the current forest fires but for the NPWS will need X amount of NPWS hubs.
Small 1 hub
Medium 2 hubs
Large 4 hubs
Major 6 hubs
They will need to use the NPWS support unit as well
Small and medium will need 1 NPWS Support unit
Large 2 support units
Major 3 Support units.
For Large and Major I would also suggest the chance for the need of dozers. Large a 40% of 2 dozers and Major a 70% of 5 dozers needed.
Now as stated above they also do law enforcement to a degree in the parks. I believe a expansion like the game wardens from the US version would work perfectly along with the training for them just renamed to Rangers and the Missions but if needed names changed to be Australian would work and wouldn't require overly much work to go and make missions just for the Australian version and won't need to make a new unit.