How do you get rare candy in Pokemon FireRed?

Articuno is in icefall cave

Zapdos is in the power plant

Moltres is on the top of mount ember

after national dex

Mewtwo is in Ceurlean cave.

raikou(if squirtle as starter) is roaming.

suicune(if charmander as starter) is roaming

entei(if bulbasaur as starter)is roaming