You have a very high chance of getting such a chest in all dungeons where you have multiple Levels on the second level, if they have just 2 levels and they are random, so for instance in the Cathedral on the second level isn't always such a chest.
They can also spawn on the edges of a map, mostly at places where you don't came arround if you rush through the game. but they can occur also in all other places on the map.
Notice that all chests arn't affected by MF any more so it is more viable once you reach lvl 60 to farm the elite packs, cause they will drop always a yellow item.