I want to make the Hayabusa armour from H3, but I could only find files for the chest piece (That worked). I have found 3d files, but the poly count is so high that even removing some of them doesn't work.
If you're wanting to take a high poly 3d model and turn it into paper or foam patterns, one thing you can do is import it into Blender and use the "limited dissolve" feature to simplify the geometry. Of course this will remove some details, but if you're working with foam it's easier to add them later. What material are you looking to make your suit from?
The files in the armory for the helmet and shoulders should be fine. The chest file is fine for the attachments, but the base h3 chest piece is very low res, so I'd recomment using a different file for that, depending on the details you want. The rest of the armor should be the same as the base armor so you can use those files for those.