Help with skin location

Okay, so the other day I wanted replace the skin for my physgun just from getting bored of it. So I go check some tutorials and ALL of them said to go to the folder location in your materials and just replace them. Guess what? THEY DON’T EXIST. None of the vtf’s exist for anything except group1 of humans. Some other tutorials said you needed to make the folders yourself, I’ve tried that. Heck I even put the entire model material folder from the source materials in there. I’ve done it EXACT to the names, locations, etc. Nothing works and everyone says its so easy. So whats up with this? Help will be greatly appreciated.