I don't have any means of getting you the exact factory hole locations (trim is already on car), but you could position the trim where you want it, mark around it and drill holes inside of your trim outline. I think the total number of clips was 14 or 16. I really can't remember at this point. Does anyone else happen to remember how many clips it takes?
You could also reference off of the points where the old studs were that you say are now missing. Can you see where they broke off at?