Using a simple server updater we can install Counter Strike Source Textures onto Garry's Mod.
Step 1: Step 1: Obtain Steam CMD
Un-Zip the steamcmd_win32.zip file into a brand new folder
Step 2: Step 2: Run SteamCMD and Update
Double Click the SteamCMD.exe program that you unzipped into the new folder. It should start to update. New files will appear in your folder so don't freak out if that happens.
Step 3: Step 3: Download an Auto Loader
Place in the folder that has everything else in it. Run it after everything has updated. IT WILL TAKE AWHILE.
Step 4: Step 4: Install the Textures
Make a new folder, Name it "CSS - Content." Go back to the folder that you placed the SteamCMD.exe program in. Open the "css" folder. Open the "cstrike" folder. Drag the "maps" folder and all of the "cstrike_pak###.vpk" files into your newly created "CSS - Content" folder. Then finally drag your "CSS - Content" folder into either
C:\Program Files (x86)\Steam\steamapps\common\garrysmod\garrysmod\addons\
C:\Program Files (x86)\Steam\steamapps\\garrysmod\garrysmod\addons\
Step 5: Step 5: Download Vpk.exe and Unpack .vpk Files
Download it Here
Drag your .vpk files, one at a time, onto the vpk.exe program. They should unpack into a "cstrike_pak_dir" folder. Open that folder once your done unpacking all of your .vpk files, Only extract the folders within the "cstrike_pak_dir" folder to your "CSS - Content" folder. Delete the "cstrike_pak_dir" and your done. It should come out to look like the picture.