Kriss, you can find the shops selling any camera equipment at the following site:
The fisheye that's designed for Nikon DSLRs is the Nikkor AF DX 10.5mm f/2.8G ED and there are some prices and stores here:
http://cameralabs.pgpartner.com/search_ ... id=3140896
It's not an AF-S which means it won't autofocus on your D40 (or the D40x), but it'll have so much in focus, it's not a big issue.
Forum member Thomas is a big fan of it, and he talked about it in the Nikon forum here: