Which part? .. The Rail Racks .. wrote an article on that on Shortline Modelers Louge - Rail Racks
The tarp is just some Magic-Sculpt (think Milliput) .. rolled out .. used some Talc (ok .. Baby Powder) to keep it from sticking. Stitching is just a razor-saw pressed into the putty while soft.
Ummm. Tie plates. That's some I had 3d printed a while back. I used the same ones on my pier ..
I don't remember who made them, but I have a modeler friend who bought etched metal tie plates. I think he got them from a company that makes supplies for handlaid track.