Plants Vs Zombies Garden Warfare - Heal Zombie

Whats the best pack to try and get a Heal Zombie to use in Garden Warfare 1 on Xbox? Last thing I need to finish all the achievements.

Internet guides on TrueAchievements say you can get one in Zomboss Down Pack but I must have opened about 30 of them and nothing. Are they only in Legends Of The Lawn pack? Or can you also get them reinforcement packs?

Any help appreciated!