Hi Stuey
Sorry for the delay in replying.
If your going to be in Sydney, just pickup a Sydway Street directory. It covers a large part of the Sydney basin. It uses an UTM grid with a AUS66 map datum, it will get you within cooeee of most caches.
They cost around $19.95 at most petrol stations, RRP is around $34 but never pay that!!! Of course thats in Australian dollars so that would be half a Euro for you.
Hope you have a good trip, give us a yell if you need more info.
Topomaps are fairly easily available from outdoors supply stockists and cover the Jervis Bay area. Cost is about $8 a pop.
Cheers
Odlid Dave