THe temple on Eilim

In the Clone Wars, Yoda said the temple was destroyed.
Where did Luke get his crystal?

 

Ilum is not the only source of crystals. Dantooine is another location that has crystals in it's caves. Ilum is just the location that the Jedi of the Prequel era ceremoniously get their crystals.

As to where Luke got his, I'm sure SOTE mentions Obi-Wan leaving instructions and spare parts in his hut on Tatooine.

 

Yup, Luke made his crystal synthetically in Ben's house.

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thanks

 

Also, the Sith make their crystals synthetically, thus giving them the red color.