Call HD. I am sure they would be willing to give you their exhaustive list of manufacturers and vendors.
If it is a bolt manufactured in the USA using Canadian or Japanese steel is it still considered made in the USA?? What about the machines to manufacture said parts? I bet if you toured an HD plant you would see Mazak, Wotan, Lagun, SHW, Matsurua, Tur, Marwin, Clausing, blah, blah, blah. What about the tooling? Most made in Germany, Japan, India, Brazil. Controls? Germany, France, Japan, etc... Is the paint and all of its contents from US soil?
I really don't think there is anything that is purely manufactured in the US. IMO to do this all materials, machine tools, tooling and controls would also have to be manuf. in the USA. Virtually impossible.