I am waiting to see what Subal says but think maybe a 28mm might be the go. Unfortunately there's one distributor in Australia & pretty much every EXR needs to be specially ordered.
Although no direct comparison, I know, the Canon 14mm on a 5DII needs a 40mm EXR. Canon's website says that lens is 94mm long & 114 degree view. Nikon 14mm is 86.5mm long with same view.
jono I used to love my 10.5mm fisheye on my D300S - nice & sharp right across the frame. Can't buy a 16mm fisheye until I can fit the port to the housing though.