Pokémon Uranium Wiki

"One variety of the mysterious Mega Stones. Have Inflagetah hold it,and this stone will enable it to Mega Evolve."

Inflagetite can be obtained from Route 10 by surfing upstream from the bridge closest to the entrance to Amatree Town (Pictured below).

Inflagetite Bridge.png
Inflagetite Location.png

Inflagetite can also be obtained if you have a Inflagetah in your party after defeating gym leader Vaeryn and you select that Inflagetah after being asked what Pokémon you would like to be able to Mega Evolve.