For online bookings, you could try wotifdotcom. The advantage of this site is that it has a grid that shows availability for a period of about two weeks in advance and you can complete your booking and make payment in just a couple of minutes and print out your voucher to present on arrival. The hotel you mention is available on the dates you want..
I note that you are in Sydney - this is an Australian site so you can ring them on their tollfree number if you have any questions and make your booking with the operator - 1300 887979.

I've used wotif before - no problems at all.