I'm not a ctf expert, but there are some people here who are interested. Keep in mind that most of us here are Quake1 players.
I am a bit surprised CTF is not a mod listed on the left, but the "threewave" ctf maps can be downloaded here: Quake Terminus
There are more ctf servers than listed on the front page server browser... click "full list" to see them all.
Typically, you have to get people to plan ahead to join, since the demand is a bit sparse.