We are actually based in Cairns but liveaboard.com are in Bali. Unless you have your spaces already reserved there are no spots left on the13th. Hopefully you have them reserved. Otherwise there are plenty of
Outer Reef trips to look at, but I agree with bowlofpetunias here that its well worth considering places outside of the GBR to dive. Personally I grew up on the south coast of Victoria and love the Bay area around Queenscliffe, Sorento etc, but I guess that's to far south to fly.
If you are set on the GBR then as I posted above book early as its peak time now and the Ribbon Reef trips are well booked out.