Are any of these servers what you are looking for?

Servers with "Coop" in the name:
n!faculty L4D2 Realism CoOp by www.arcor.de
[GER|PFC] Schulhof coop only
Anitalink.com Left 4 Dead 2: Coop 16x
Anitalink.com Left 4 Dead 2: Coop
[FR]-[L4D2]-[iNDEPENDANTS]-[COOP]
OptiZone.RU L4D2 Coop #1 v2.1.2.2
Twilight Editotaku COOP
Suedside Zocker - Coop
4 SIMIANCAGE [HARD] COOP 10 player
[GFLClan.com] 20 Man COOP|NoLag|Chicago