There is a new custom Left 4 Dead 1 campaign released this weekend called Dead Before Dawn. Dead Before Dawn features Crossroads Mall as a replica of the mall in the movie, Dawn of the Dead. Originally created for the HL2 Mod, No More Room in Hell but has since been undergoing major changes to be ported to Valve’s Left 4 Dead.
The download of this custom campaign is about 1.1GB and can be downloaded through ModDB, SNT at University of Twente NL or through Torrent.
Once downloaded just place the files in the /common/left4dead/left4dead/addons/ directory within your steam folder.