Where exactly did you look for the scout chest piece? I see two of them in the database, one with just the attachment, one with a render of the entire chest so that people can just input the appropriate scale factor in and have the piece automatically scaled to the chest piece. I just downloaded, and opened, both files. Just go to 405th.4shared.com (or use the link in Katsu's sig), click "Halo 3 Database," "Spartan Mark VI," "Chest," "Scout" and poof, two chest files, both unfolded, both quite accurate to the in-game model.
As for the EVA, afraid I can't help you there.