It's probably worth looking at this from the employer perspective, then you will get a better understanding what is required of the employer when they sponsor an candidate for a work visa.
Unless the job function is on the
Migration Occupations in Demand List (MODL) then the employer will need to show that they are unable to hire an Australian resident or citizen with suitable qualifications and experience.
HR functions are not currently on the list (they were a few years ago).
A possible exception to this is if the employer is a pre-qualified migration sponsor, this means they are allowed to sponsor a pre determined number of migrants each year with minimal justification. However, I'm not sure if they can use this for skill sets that are not on the MODL, and even if they can they probably wouldn't want to do so for a skill set that is not in short supply.
That said, the demand situation in Perth or wider WA maybe different from the east coast of Australia, because of the growth in the resources sector. So your best chance of success may be in Perth or regional locations in WA.
Personally I would approach companies directly rather than applying through recruitment agencies who will probably give preference to candidates who are already Australian residents/citizens.
Also, when an employer sponsors a migrant they have to accept certain liabilities and there are also additional one off costs plus their own admin costs. So you can see why employers will only sponsor people for a visa when they really have to.