Steam – Garry’s Mod Steam Server

I followed the following instructions for setting up a Garry's Mod server in Linux via the command line;

http://wiki.garrysmod.com/page/Hosting_A_Dedicated_Server

 mkdir ~/Steam
 cd ~/Steam 
 wget http://media.steampowered.com/client/steamcmd_linux.tar.gz
 tar -xvzf steamcmd_linux.tar.gz
 ./steamcmd.sh +login anonymous +force_install_dir ../gmodds +app_update 4020 validate +quit

Then I can run it with ./srcds_run -game garrysmod +maxplayers 32 +map gm_construct

I can launch and play on my Garry's Mod server now, but how do I get additional game modes and maps? I really want a server running the game mode Murder on CS_Office but I can't figure out how to do it.

I have Counter Strike Source downloaded, but the maps haven't appeared in the maps folder. I also don't know where to download Murder from.

I can change the game mode to Trouble in Terrorist Town but only because it came preinstalled into the gamemodes folder, I'm not sure where to download other game modes though.

Thanks.