Camera Geekery: The Nikkor 6mm f/5.6 Fisheye Nikkor aka The Holy Grail - Japan Camera Hunter
Nikon 8mm f/2.8 Fisheye
Nikkor 6mm f/2.8 fisheye lens video and photo samples - Nikon Rumors
DSC04841 edp | Testing Nikon 6 mm f/5.6 Fisheye-Nikkor on So… | Flickr
This Uber-Rare Nikon 6mm f2.8 Fisheye Lens Can See Behind Itself - The Phoblographer
Ridiculous Lens: Return of the 6mm f/2.8 Fish Eye in Photo Insider Blog at Unique Photo
Lensfinder.com - Ultra Rare Nikkor 6mm f/5.6. Only a few hundred of these lenses exist. This lens has a 220 degree field of view for Full Frame 24x36mm sensors. Made in Japan
Not for the frugal fisheye photographer: Rare Nikon 6mm f/2.8 Ai-S lens available on eBay for around $85k