Where to get TM 29-psychic in FireRed?

You can't get TM29 - Psychic in Pokemon FireRed. It's not available in the game.

The move Psychic is only available to learn via leveling up for certain Pokemon in FireRed. It's also available via the Move Tutor, which is unlocked after beating the Elite Four and can be found in the Pokemon Center in Fuschia City.

However, keep in mind that the Move Tutor doesn't offer Psychic as a learnable move.