Help! I can't use any CS:S content in Gmod!

Every time I open Garry’s Mod (v10), the only content available for use is the custom content I downloaded from and the content from Half-Life 2 and Garry’s Mod. But, I also have Counter Strike: Source and Portal installed on my system, as well as HL2: Episodes 1 and 2. Shouldn’t those maps and objects appear as well?

My Machine is an Athlon X2 DC 3800+ with an Nvidia Geforce 9600 GT
with 4GB of DDR2 in the rig running Windows 7 Professional 32-bit.

Do you own CS:S? As in bought from the steam store?

Yes. The rest of the games (bar Gmod) were bought as part of The Orange Box.

Gmod settings, Mount addons you want

Thank you, good sir.