Hi, i'm another Aussie who's recently joined the ranks of happy Axim owners.
I recently bought a Netgear CF WiFi card from OfficeWorks for $179 but later discovered that Organiser World (pda store in Melbourne
www.ow.com.au ) is selling the same card for $139

But the card works great though - I can access the internet via my office network and at home with minimal configuration.
You can get cheap memory (SD and CF) from the Melbourne Computer Market (do they have similar markets in other states?)They are currenly selling 128MB SD for $80, 256MB for $150. (and it works fine with the Axim) Other than that, I haven't found many places in Australia that sell PDA accessories.
But I have found some reasonably good deals from the States:
Bluetooth CF card for $49.99 US - Semsons & Co, Wireless IR Folding keyboard - $49.99 US - Moonlight Technologies, Metal (Aluminium) case - $29.99 US (excellent case - it does a great job of protecting your Axim and it looks cool too!)
I've also bought a screen protector from Box Wave - claims you can wash it and re-use it, anti-glare, fingerprint free, improves handwriting recognition, dust repelling etc... I'll let you know how long it lasts.
I hope this has been helpful.