To get to Plantation Island you will need to book transfers with Malolo Cat. They will pick you up from the Airport and take you to Port Denaru. From Port Denaru you will then catch the ferry directly to Plantation Island Resort.

Please find the timetable here https://malolocat.com/timetable/

Flights from Sydney to Nadi (return) can be booked through Fiji Airways.

Flights from Sydney to Nadi (return) can be booked through Qantas.