Where can I find a ISO download of Darwin? I downloaded Darwin at one time (even after they stopped releasing the ISOs) off of Apple's website. Unfortunately, I have no idea where the link went. I had it at one time.
Try the PureDarwin project.
The goal of this project is to make Darwin more usable by providing an installation ISO, documentation, and add-on software.
I don't think you can directly get a copy of Darwin in an ISO format. There are some channels setup to get the source code but you're not going to get a usable installer and operating system without going to a community-supported project like PureDarwin.
You're not going to find this because the OpenDarwin project shut down 5 years ago. OpenDarwin is so dead that I had to make that link using the Wayback Machine, since the original sites related to this project have all been shut down, too.
This is probably what you're looking for: http://web.archive.org/web/20070423174905/http://www.opendarwin.org/downloads/7.2.1/OpenDarwin-7.2.1.iso.bz2