Where do you get Torchic in Pokemon FireRed?

This is one way. Trade it from Ruby/Sapphire or Emerald.

TORCHIC: First, you need a Wireless Adapter or link cable. Then, connect it with your friend's Gameboy ADvance/SP. Your friend needs a POkemon Ruby/Sapphire Version. THridly,Both of you should have the Wireless Adapter or link cable connected and then go to a Pokemon Center and then go to the Second Floor and talk to one of the ladies there. If both of you are now on the second floor, trade! And there you go! A Torchic in your Party!

P.S

Your friend's starter Pokemon should be Torchic!

Hope I helped!

Or you can beat Red and then the credits will roll and when they're over you can go to Saffron City and go to the Silph Co. building and you can talk to Steve on the main floor with the blue hair and pick the Red stone and he'll give you a Torchic. Make sure you have room for it