How to download materials

I'm sure I'm missing something here, but where/how can I download more materials for Twinmotion? I know there are built in materials like "hammered copper" for example, but where can I find a "hammered chrome", for example? Or perhaps a "gunmetal"? I know I can apply, copy, modify, then rename materials, but is there some quicker way to have tons more options in my material library? Thanks in advance :)