I noticed this problem the second I tried spawning the drunk combine thing I had recently downloaded. After I checked on the forums, there appeared to be no fix. So, I tried my own method of fixing missing textures/models.
Here is a copy/paste of what I wrote on Leet Lounge forums.
To do so, start up CSS to the main menu. Then, exit CSS.
Afterwards, download GCFScape and install it.
Goto Steam/Steamapps and look for Counter Strike Source Shared (The larger of the two css gcf’s)
Exact all the models/materials/textures/sounds to your desktop.
Once that finishes, goto Steam/Steamapps/ACCOUNTHERE/Counter STrike Source/cstrike.
Put all those folders inside the cstrike folder. If it asks to overrite, click YES!
Note: If you don’t have a CSS folder at all, extact all of the counter strike source GCF’s and place them in your account folder.