You have several options to choose from:
Internally transfer from any other degree in Macq Uni. I think the GPA requirement for B Chiro is 2.5, so as long as you have that you will be able to transfer into the program. However depending on some subjects you do, they will not count towards your degree.
Externally transfer from another uni. Go through UAC and compete with the next batch of HSC grads for a place. However you have to wait till end of year, but internally you can apply mid year (and its also for free).
Non-Award. Not really too sure about this one, but the general gist of it is you choose a random subject (paying the full price) and if you get a credit they will let you into a degree. Whether or not the chiro department accepts you straight into the program, Im not too sure. So you may have to transfer internally.
The most costly option is to get another bacherlor and then apply for the masters. But before you are allowed into the Masters program, you need to go through a qualifying program where they make sure you have taken the necessary subjects (for required knowledge). The qualifying program is full fee, so depending on what degree you graduated with can be very very very expensive.
Yet you are only doing your hsc this year. The UAI cutoff for chiro is not that high ~mid 80s or so. You are probably better off applying directly into the chiro program if you are ieally interested.