The fastest way to get here is to start at Betrayer of the Horadrim: The Forgotten Ruins quest as it drops you right in the middle of the Oasis. The Liquid Rainbow is always dropped from the Mysterious Chest (which looks like a Resplendant Chest) however, the Mysterious Chest will not always appear in the Mysterious Cave.
Save Zaven the Alchemist from a few ghostly attackers and he will open the Mysterious Cave. Liquid Rainbow - Spawns in the Mysterious Cave in the Mysterious Chest in the Dalghur Oasis, Act 2.Shinbone - Spawns randomly in the fireplace in Leoric's Manor, Act 1 (Is not required to craft the 'Staff of Herding' in the console version).Black Mushroom - This spawns in Cathedral Level 1, Act 1.(the following components can be found on Normal difficulty) You must create a Staff of Herding to find Whimsyshire.