If you want to do it with incandescent bulbs one trick is to keep the filament heated when off. In other words don't turn them right down to zero but leave some amount of power on to keep the filament warm but not to show noticeable light.. This way the filament will heat up much quicker and give more of a flash response when you increase the power quickly...Of course I have only seen this done on pinball machines flasher lamps but it should work for outdoor lights.....
How about this idea. To be honest it might be possible.Thinking of using a car headlights, since they work on 12 volts dc...The plan would be a MR16 be the controller and depending on the amps draw of a headlight (I didn't look that up) you might have to use a 12 dc relay to handle the higher amps if required.Rick R.btw: Use the High Beam lights of course