The Power Company website has a training program for increasing core strength specifically for climbers. It is:
“Front Levers (to failure)Do not hold the levers. Go to the top of the motion and lower immediately, slowly. Do not initiate any swing. Maintain good form, and when form breaks down, stop.Pushups (double the number of levers completed)Begin immediately following the levers (supersets), with no rest between. Maintain good form, and complete the full range of movement.3 sets of the above, with 2 minute rests between sets, and after final set.
Hanging Swivels (to failure)Go to the top of the motion and lower immediately, slowly, and all the way back to a hang, without swinging. When form breaks down, stop.
3 sets of these, with 1 minute rests between sets. “
He has more details about the program here.