Getting corals to spawn in your tank for the most part is a very difficult and complicated hat trick to pull off. In most cases it is triggered by a very specific set of water conditions and is based around the moons lunar cycle. The amount of eggs and seamen expelled in the tank will often pollute the water severly. Many of the techniques we use in our tanks is counter productive to any coral larva surviving. Skimmers and filtration systems will contribute to substantial loss in viable coral larva before they have a chance to settle in the tank.
There are some exceptions to this though, as Tubestrea corals (Sun Polyps) can some times successfully spawn in a tank. This is still pretty tough to do though, but realistically possible.
At this point, given our current husbandry skills and technology available Fragging is still one of the better ways to create more corals. This technique works better on some corals more so that others.