Currently science has found no foods that will stimulate and increase the production of more semen. The only thing that will help would be better overall health. Good excercise is the key in that when you are healthy your body works faster and harder, thereby producing more semen that you desire.
Eat foods that are high in protein and low in fat such as fruits, vegetables, and grains. Oysters and celery are particularly good for this. Make sure you steer clear of alcohol and caffeine to ensure a strong sperm count.