WoWDB

The boomstick, launcher, and bomb become available during the last stage of the scenario. The power-ups spawn within the walls of the fortress that you are defending, so there is no need to explore the whole map. Some of the power-ups spawn in obvious, open locations. Other power-ups spawn inside of buildings that are on fire, which can obscure them at first glance. Do not dawdle in the doorways of flaming buildings because the fire will damage your character. Power-ups may be collected after the scenario is complete.

Important: Your character must NOT be mounted in order for the power-up to buff your character and thus count toward the achievement. I learned this the hard way.