Easy, you won't always get what you want in 20 minutes.
I've not seen pep files for this before but I know of Space Marine 3D meshes(models) at TurboSquid.com. Maybe you could start there? Unless someone else know of pep files.
there have been a couple people that have done the costumes and due to the fact power armor shoulders are so massive when scaled for a human, its quite uncomfortable to wear.
Nimba Creations did some promotional stuff, and some costumes for a short film few years back.
I've spoken to one of the guys that worked on the ultramarine costume(in emails), It was sculpted in foam, sealed, detailed then they took moulds and cast the parts, I cant remember if he said they were urethane or glass.