Crystals can be found at Barren Temple north of Facade on collected items.
Although you can also buy them in the second half of the game, if you are in Facade, for this you will have to access the materials store next to the king's mansion, where you can buy them for a price of 2,400 G.
If your problem is not money and what you want is to have an upgrade of weapons you can buy them, but if on the contrary you find yourself short of money the best option would be to grow the crystals in Barren Temple, which as you can imagine will take something more time. And finding it is not entirely guaranteed, but it is a good option when it comes to saving money.
If you have already read this article, I hope you know where to find crystals in Nier Replicant Ver1.22 and you can choose the form that best suits what you are looking for in the game, so go for it.
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