I don't think it was ever released. According to the review on TheDigitalBits.com, Bill Hunt mentions that FOX thought they were being perceived in a negative light, and cut the footage by an hour. There are apparently several sections of the documentary (most notably "Production: Part III") that were severely edited. The review mentions there's a cut BTS clip where Fincher is sitting in a chair, looks exasperated, then grabs a nearby microphone and makes a sly comment at the suits at FOX. If anyone knows about this, it would probably be Bill Hunt at that site.

I have some of the old workprint footage that wasn't put on the Assembly Cut, but I don't think it's all of it. I had gotten it off Youtube, but it's very small and not good quality. I also have some text articles as well, but I've been more focused on collecting information and video for a possible project.