Step 1: Install Counter Strike Source, dont put your computer at risk however by downloading from a sketchy site. Read this guide to be safe. https://steamcommunity.com/sharedfiles/filedetails/?id=1282064537
Step 2. Still seeing missing textures? mat_specular 0 is your command! You can enter it by pressing ` or whatever you've assigned the key to.
If this doesnt help you might need something else, which your probably better contacting the forums than me.