Cards are your friend going for this. Pick an unlimited arrow of your choice (I picked grenade) and hold up in one of the offices at the end of the upstairs hallways. I got all 3 nightmare achievements on my first run. Enemies will keep spawning while you are in the office and stop for a bit when you leave and clear out what has already spawned.
You can get this over several playthroughs, but one should be more than enough with unlimited arrows and a few extra minutes.