fabien-michel offers the very large and excellent AmbientCG texture library with 1500+ textures, among which many metal textures: https://github.com/fabien-michel/sweeth ... g/releases
For Sweet Home 3D the most fitting is the 256 or 512 library but if you insist on a high resolution texture you can also download the 1024 version.
Import the texture library: Menu > Furniture > Import textures library
The full list will be available in the modify furniture dialog when you modify materials.