I also have the UK MARTIN DVD with the German DAWN thing (which actually runs for 23 minutes PAL) and the downloaded VHS->DivX of the Incredibly Strange Film Show episode (38 min PAL).
I also have a DVD conversion of the Tom Savini Scream Greats laserdisc that I made myself but that might be pushing the limits of a DAWN-orientated set (just a few shots borrowed from Document of the Dead). I may spruce it up with menus some day and pass it on as its own thing as its alotta fun.
There's a million articles on DAWN out there but one that might be of particular interest is the Tom Savini story from Fangoria #1. I'd be happy to scan it if there's any interest.
Apparently the German trailer features footage not found in ANY version out there. Just a few shots, however. As for a composite version incorporating ALL known footage, I recommend contacting the Mall of the Dead webmaster. He apparently started work on this project sometime ago. I'm unsure how far he has gotten but even if he has abandoned it, he may have some valuable advice for anyone else willing to take the challenge.
You might also wanna post a recruitment drive at the Homepage of the Dead forums for material. Alotta hardcore Romero nerds hang out there and I bet that, combined, they've probably got everything there is to have on DAWN (including, as I understand it, the 'needle drop' library music cues not available on any soundtrack release).