I need to get the consciousness shard region likelihoods into the game, but I will say this: they are identical to those of the gem veins. So if you want to know, in the short term, where to find yellow consciousness shards: look where to find yellow citrine raw gems, and it's identical.
The one exception is enemies: enemies drop shards of colors based on the type of enemy (what makes sense for that enemy type, mainly), and so those vary from place to place and won't match anything else. It's the actual caches of shards that you find that vary by region, and they're also the most reliable and quick way to get shards.