don't have my materialsystem folder, how do I get it?

[stoopdapoop]

I started work on a mod based on hl2 single player a long time ago. and when I recently decided to (try) to get into shader authoring, but I don't have the materialsystem folder in my src folder. Is there an easy way for me to get it? D:

will starting a new mod, and copying over the folders work?