We used some old, discarded very lightweight sides for a gazebo while we waited for our sun busters.
I just happened to be loading stuff for the dump, the old gazebo was in the pile and I noticed the side bits. Hey presto! They almost fitted.
I'd be a bit inclined to check the measurements on the BCF or Supercheap (or similar) gazebos. And BCF sell side walls as well, or they do in Qld.
Or grab some shade cloth and just cut it and use those tent clips to attach.
If it's a temporary measure and does the job, beauty and perfection can come later.
I do know Brisbane Camperland have the grey side walls ( Coast to Coast brand from memory) which do fit....and they're on special. It may be possible for them to post to you in time for departure.