where can I get the bush walking trail or map in Australia national park?

I am intending to go to Cattai National Park

Any local tourist information center should have maps of the local trails.

The following paragraph gives a general summary of the tracks from the NSW Government:

There are presently only three constructed walking tracks within Cattai National Park: a track which passes through the rainforest on Cattai Park, a track from the silos to a lookout on the Hawkesbury River, and an interpreted loop walking track on Mitchell Park. A number of informal routes follow existing bridle trails while other walks rely on visitors following maps on brochures. These informal tracks do not necessarily follow the most scenic route or commence from car parking areas and need to be incorporated in a formal walking track system for the national park.