Left 4 Dead 2 Models

I just got Left 4 dead 2 but I want to know how I get the left 4 dead 2 stuff for Gmod
I have seen youtube videos of Garrys mod with Left 4 dead 2 stuff in it.

So How do I get the Left 4 Dead 2 models, I really want to use them badly
Do I have to do something with the files?

Note: I am Australian, so it may have something to do with the Cenor