I searched a long time too , till I found Mycom stock them (Comptech not !)
AS you can see from the photo, pretty small, slighty bigger than the 2,5 inch harddisk, it runs on 5V, 2A adapter, I use it in my car on a Ipaq adapter no problem, sure Mycom will ship to Australia against costs, though it should be available soon everywhere
Bought mie without HDD (E 129)
You can swith it off via the webinterface, all switches are at the front,
power on by recycling the power or by the switch; nice if you do'nt use your car for a long period as it will drain the battery after 1 to 2 weeks
Only problem I found, when connected both wired and via WDS , your whole network performance goes down, which is logical, has even it's own DHCP server build in