Lyn is correct -- HAL Zaandam has a cruise leaving San Diego on October 30, arriving in Sydney 25 days later; it can also be extended to 39 days if you also wish to visit New Zealand. You can find details on the Holland America site
For a cruise of this length and itinerary, I highly suggest that you consult with a travel agent who specializes in cruises. We are not permitted to recommend TAs here, yet you may find one who is accredited by Cruise Lines International Association by going HERE
and using the Cruise Expert Finder a bit down on the right.