In Central Sydney...

 Where should I go train, Ideally Id like some no-gi grappling, but gi is fine too in a pinch. MMA classes also a plus for when I've shaken off the jet-lag and rustiness....

www.BoxingWorks.com.au

Can't get much more into the centre of Sydney than there. :-)

www.lionsdenacademy.com.au
On the same train line like the airport, you can jump there as soon as u get off the plane lol ;)

I trained at Boxing Works on my trips to Sydney, It's a great place to train, lots of good guys there and an awesome instructor - Rodney Ellis.