Its really simple to get, you would have to buy a glass jar (small medium or large/very large)
You would only find it within the clockworks
T1 only would find small liquid amount. small liquid restores 10 energy.
T2 would find medium and small. medium restores 20 energy.
T3 would find large and very large. large restores 30 energy, very large restores 40 energy.
It would have a chance to drop off a giant lichen colony for T2 and T3, self explanatory reasons.
You could find it red chests, a reward for the end of an arena, or a end of boss reward along with your tokens.
There are reasons CE does not drop from the Clockworks. We already get crowns, materials, and sometimes equipment; free energy would not help. Especially since it can drop from an easily and commonly encountered enemy or where rewards are plentiful as they are already.
This is basically the same as previous suggestions to have small mist tanks drop in the Clockworks, all of which were defeated and beaten into various colors of the rainbow.