"Tyre recommendation for 15 inch wheels"
Problem is getting the right size for the rears.
 
A Google search turned up these, anyone tried them?
http://www.jaxquickfit.com.au/tyres/brands/pirelli/p-zero-asimmetrico
205/50R15 and the scarce 225/50R15 size are listed
BTW treadwear 220
 

Toyo R1R are good but will tend to overheat quicker than the others due to the tread design. The small tread blocks move around much more and will overheat and start wearing down quicker at the track. Would be good for wet though.

Hi Rick,
 
I will have a set of 16' Enkeis available if your are after other wheels.  Not 17's but good light wheels.
 
I just purchased another set of 17s.

According to the rules, wheels must be oem sizes for unmodified street class, so i might as well get 17's rather than 16's. I imagine it wont be long before 16's are hard to get too.

Thanks everyone for your ideas and help, but it looks like i'm saving for some 17's....... 
 

Call up your tyre dealers and ask if the have any Toyo T1r's. They would do both front and rear in the correct sizes if they have them in stock.

A lot of people here will call it blasphemy for even suggesting it, but I can actually recommend going to eBay tyre dealers. There are a couple based in Sydney that have proven to be pretty good for me. I've used them twice for tyres that I've taken to the track and thrashed and they performed exceptionally well.
I did a quick search for your sizes and came up with a 205/50R15 for the RSR's, which I can personally vouch for, and the 225/50R15 offered up a Toyo R888, which are pretty good, or so I hear.
Or, as several people have said, move up to 16's or 17's, where tyres are easier to find, but also tend to cost more.
I can also guarantee that, even though you're up in Ceduna, it'll be cheaper to freight a set of tyres to your door from Sydney than to buy from your local dealer, as they mark up prices a LOT. Got quoted ~$300 per tyre for RSR's at a dealer, bought them for $155 each on eBay, and delivered for $50.
 
I'd suggest going to a dealer only to fit your tyres, and even then, take the wheels and tyres separate to the car. I've seen too many ruined studs and new unexplained dents after taking the whole car to trust them myself, and I work in the industry.
 
If you plan on keeping your original wheels, or even upgrading to a larger wheel, let me know when you're after tyres. I could probably hook you up and save you a few hundred :)