Hi Simon,
You can actually make these fairly easy yourself.
You'll need to clone a working locomotive and tender, along with the bogies, yourself and convert these to a static scenery objects which you can then place together. Using a photo-editing program such as Gimp, Paint Shop Plus, or Photoshop, for example, you can then add extra rust and dirt and 'ruin' the metal to make the locomotive look like its ready for the scrap pile.
I've done this before to create some equipment for a museum on one of my routes.
John