What bulbs are in the front ,if its they are those low wattage ones they may not be drawing enough current therefore fast flashing as if theres a bulb gone 
Very good point. Check the wattage of the bulb from ebay. Just to confirm, it is only one side that isn't working properly? The one that was hit? If so, check the bulb, then start swapping lamps from the affected side to the working side one by one, front unit, side repeater then rear cluster. hopefully you'll pick up on something there otherwise you will be looking at a power/wiring fault as already mentioned
