You can get approvals (in some cases) from the State/Territory Authorities to operate in National Parks if you write to them. I've got an approval to use my drone in some national parks in the NT, lots of restrictions and prohibited (no fly zone) areas. The approval was free and very easy to get, noting that the Part 101 rules still must be fully complied with in the park.
Most Councils also have restrictions with regards to drone operations in parks and reserves, even if the CASA App says that its ok to fly at the location. It pays to check the Council's website or call them if in doubt.