Applying TF2 skins in Garry's Mod?

See this skin here?

How would I apply that skin to the TF2 revolver world model in Garry’s Mod. Where would I put the files? I didn’t put this in the Help & Support forum because this isn’t a “troubleshooting” kind of thread, at least, I didn’t think it was.

Same as you’d do with TF2. Materials/Models.