WELL... funny you should mention this.
I have the set of L4D files and Steam servers to go with that, when used in conjuction with UCL to launch it, will let you browse the network for servers etc.
I mean, this is for people that have legitimate copies of the game but steam's screwed up for them only... but you know

(also comes with a setting to let me auto-spawn lots of tanks with the click of a button, without cheats. It's great!)
--edit--
It is an older version, as the latest version doesn't seem to work with UCL anymore.