Hey!
Booklists should be released when it gets closer to the start of semester. Some degrees might have already released their booklists on their faculty websites. Otherwise, you could check here -->
https://www.bookshop.unsw.edu.au/textlist.html
In terms of buying textbooks, I think it depends on your faculty. Facebook has many UNSW Textbook Exchange Groups, but not for all degrees and faculties. The common ones I see are mostly law, commerce and engineering. Alternatively you can buy second hand textbooks from Gumtree (might be hard to find) or StudentVIP. Zookal is also a good place for cheap new textbooks. You could also try searching up your [Textbook name] or [ISBN] and add PDF to the end of your search on google if see if anything pops up [if you're looking for a soft copy].
Also, I think its best if you wait until your first lecture before you buy any textbooks. Sometimes, the materials you get in your classes are sufficient enough to get a good mark, or you could hit up older year students who may be selling them on campus. There's also a UNSW Bookshop on campus and a Library if you are just looking to loan.