Pretty sure you're not allowed to put caffeine in painkillers at all in Australia. I've certainly never seen it that I can recall. It sounds like an inherently dangerous idea to combine stimulants and depressants.

Also, you can get codeine over the counter here. You need a prescription for the higher strength stuff but you can get strong enough codeine without one. The pharmacist will ask you a few questions about why you want it but I've never been refused it. Costs 7 or 8 bucks for 20 tablets of the name brand stuff from memory.