The player can obtain the Lucarionite by completing Mission Card 2.
The Lucarionite was also available as a prize during the Mega Lucario Competitive Stage. This Competitive Stage ran on the Nintendo 3DS version from March 15 to 22, 2015; May 18 to 25, 2015; July 13 to 20, 2015; and January 30 to February 6, 2018. It ran on the Pokémon Shuffle Mobile from December 1 to 8, 2015; and January 30 to February 6, 2018.
The Lucarionite enables the following Mega Evolutions:
A Lucarionite made its physical debut in The Cave of Trials!, where it was found by Korrina in a cave near Geosenge Town. After battling a Blaziken guarding the Lucarionite—which was later revealed to belong to Korrina's grandfather, Gurkinn—Korrina obtained the Mega Stone and used it to Mega Evolve her Lucario. The uncut Lucarionite was later set in an armband by McGinty, allowing Lucario to wear the Mega Stone.
Another Lucarionite appeared in The Aura Storm!, under the ownership of Gurkinn. Much like Korrina's Lucario, Gurkinn's Lucario also wears its Lucarionite in an armband on its left wrist.
Korrina possesses a Lucarionite, which first appeared in The Aegislash Agenda. It was later revealed that she and her Riolu had found the Mega Stone together in the past, as a task set by Gurkinn in order for her to become a Mega Evolution Successor.