So I recently came across this, which is a standalone game as you only need Source Multiplayer 2013 to play it.
It is essentially Space Marines Vs Tyrannids, with both of you trying to advance and capture objectives while defending your own.
Several playable classes, including Terminators, Lictors, Carnifexs.
Plays rather well, probably the best source engine fps game I've seen actually.
http://40ksource.com/