Few days ago Qqshka added support for cooperative game mode in KTX so you can actually play the normal single player campaign in KTX server if you wish to. The command for this is:

/votecoop

And it also disables cooperative game mode once you're finished with it. I'm sure there are some bugs left in the code (like players telefragging each other after map change etc) but feel free to test this, you can find servers that support coop from:

gibbage.mine.nu:28501 ->
wargamez.dk:27501 ->
qw.intarweb.dk:27501 ->
qw.suomicom.fi:28001 ->
troopers.fi:28001 ->

Report any bugs/feature requests here.