Try
http://www.bodybuilding.com/fun/drobson263.htm out or go with something like the following...
Monday
1. Crunches
a. 50 x Bodyweight
2. Swiss Ball Hyperextensions
a. 30 x Bodyweight
3. Good Mornings
a. 50 x Bodyweight
4. Russian Twists
a. 50 x Bodyweight
5. Leg Crunches/Bicycle Crunches
a. 50 x Bodyweight
6. Side Bends
a. 30 x 50% 1RM (15 per side)
Wednesday - Complete as a circuit a total of 2-3 times with 90 seconds rest between each circuit
1. Workout Ball/Swiss Ball Crunches
a. 15-20 @ 40% 1RM (Plate)
2. Side Bends
a. 15-20 @ 70% 1RM (Dumbbell)
3. Leg Raises
a. 15-20 @ 60% 1RM (Dumbbell)
4. Good Mornings
a. 15-20 @ 70% 1RM (Barbell)
5. Hanging Leg Raises
a. 15-20 @ 50% 1RM (Dumbbell)
6. Workout Ball/Exercise Ball Hyperextensions
a. 15-20 @ 60% 1RM
7. Russian Twists w/ Medicine Ball
a. 20 @ 15lbs
8. Bicycle Crunches
a. 20 @ Bodyweight
9. Workout Ball/Swiss Ball Side Crunches
a. 15-20 @ Bodyweight
Friday - Same as Monday...
This should build your core quickly and you will for sure feel it. Dedicated core days I believe should be done for all fighters as it is by far the most important for more reasons than can be named.