I was also looking for a natural keyboard for my G4 - seanyepez told me about Adesso. If you email them they'll get back to you fairly quickly as to a distributor where you are - you're in Sydney? Then try the Apple Stores on Sussex or Clarence Streets. Don't bother with StatusGraph - they're the most unhelpful grouches around.
I didn't buy one as I am waiting on the 'ice' version which hasn't arrived in Australia yet. The only version available is green - or it was 3 weeks ago and if it isn't black, gray or ice then it doesn't get connected here!
Check out their products at
http://www.adessoinc.com/.
I also had a look at the Microsoft Natural Pro which has a whole range of internet and sound buttons but there is no driver for these (M$ were very unhelpful) and no power button.
Finally, try using google to do a search on keyboards - the possibilities it comes up with are endless.
I swear by the split keyboard - they take a small amount of time to learn and once you've used one you'll never go back. I even bought one for my work out of my own pocket - ok, $49AUD for a M$ keyboard is cheap but it *feels* good.
cheers
Simon