I'd contact the Confederation of Bushwalking Clubs in NSW. It will either be them, or they'll know who it is that looks after that log book and will be able to organise a replacement.
I got an email back from the Confederation of Bushwalking Clubs confirming they had passed on the fact it was full, but I have no visibility of any plans to replace it.
I reckon if anyone is planning a trip there in the next month or so, it would be good if they brought along an A4 book to place there, if a proper replacement hasn't been made yet.
There's a club trip going there this weekend so I'll mention it to the leader. If I hear back I'll follow up this post so we don't end up with half a dozen, not that that seems likely
I saw some photos on Facebook from a party that went out to Mt Cloudmaker last weekend to replace the logbook (Thanks Wyn and friends).
I also heard that the Knights Deck logbook is full - if anyone is going out that way - they may want to buy a small book to replace it (I seem to recall the container there is pretty small?)