Unless it can be had from a high level grotto blue chest I think the only way is alchemy. No monster drops it, it isn't in any red chests, it isn't a quest reward, you can't buy it in a shop, and you can't get it from turning in mini medals. I don't know of any other way to acquire an item. I'm assuming you're postgame, and then I can offer the following for help on gathering materials, WITHOUT farming them:
To get the ethereal stones don't start from scratch... If you're at the end game you can do quest 60 to get an enchanted stone MUCH quicker than it would take to gather the ingredients. And I believe that it is repeatable. You must be in postgame to access it though. These upgrade easy through alchemy to ethereal stones.
The chronocrystal must be bought. (unless anyone else knows of a way to get one?)
Sainted Soma is harder. You can get the lucida shards from quest 61, which is repeatable. Again only accessible post game. I believe quest 38 gives you an Elfin elixir the first time, but a sage's elixir upon repeating. Finally, Quest 121 yeilds (DLC) an astral plume and is also repeatable.
I just got the quest where someone wanted one, and I didn't feel like farming the harvest points to make one. The above way still takes a while... It just relieves the boredom by switching it up.
Use the quick save technique on S rank blue chests for sainted soma is the fastest way, depending on your views on where that falls in the cheating spectrum. Other then that get a map with a lot of S rank chests (lol) and run that repeatedly, 10% drop rate or so. Chances are any map with S rank chests has lots of A and B that can get Astral Plume, Sage's Elixirs and Ethereal stones which are the main things you need. And check the overworld every 4-5 game hours too...
Then do it 4-20 times per item depending on your is hoimi cheating views.