I have a mated pair of Clarkii's who have been laying eggs every 2-3 weeks for about 5 yrs now. The male guards the eggs for about a week or so and they hatch at night. The eggs start out orange and turn silver as the fry mature. After seeing alot of batches, it's pretty easy to tell when they are going to hatch. When they do hatch, the fish in my tank get a good nutritious meal.
Raising clownfish fry is A TON of work. I suggest you do alot of research and see how involved it is. Then try find a place that will buy them from you. Fancy, high dollar fish and/or hybrids would be alot easier to sell than any commonly seen clown.
You can get some good basic info here.
Breed Clownfish | Saltwater Fish Breeding