They most likely discontinued it because it used the battle cow version of the cold ones.
As for people who need to make more than one, use a box of cold one knights, and a box of tomb king chariots. Then convert some guys up to crew it. So if you do all that, it should take 2 boxes of knights, 1 box of chariots, and 1 box of warriors. The 4 extra knights can be made into extra models for a normal unit, so you can choose whether or not to use various command options. The 10 extra warriors left over is exactly the number of guys that should be a RxB unit. So with a bit of planning, there should be no waste.