If you're missing a map,go to this link, press CTRL+G and type the map name,then click on it. It will automatically start downloading.
After the download is done,drag the bsp. file to

Have fun playing!

If you're missing a map,go to this [url=http://fastdl.friendlyplayers.com/granny/maps/]link[/url], press CTRL+G and type the map name,then click on it. It will automatically start downloading. After the download is done,drag the bsp. file to [spoiler]C:\Program Files (x86)\Steam\steamapps\common\GarrysMod\garrysmod\maps[/spoiler] Have fun playing!