I've had a hard time finding any copies of assault on ulthuan for MSRP. Pack are only going to get more scarce because FFG is loosing the warhammer license.
Your best bet is to find someone auctioning their copy of the game off and selling the extras you don't want.
I haven't been able to find Assault on Ulthuan copies going for less than 200 at all. (Well, one going for $190 on B&N's marketplace, but still.)