Raichu locations — where to catch

In Lumiose City (Legends: Z-A)

• Quasartico Inc. — Trade
• Wild Zone 20 — Walk

In Paldea (Scarlet & Violet)

• Casseroya Lake — Walk
• North Paldean Sea — Static Encounter
• Socarrat Trail — Walk

In Hisui (Legends: Arceus)

• Golden Lowlands — Walk
• Space-time distortions — Walk

In Kanto (Red, Blue & Yellow)

• Cerulean Cave — Walk
• Kanto Power Plant — Walk

Other games (4)

• Sword / Shield — The Isle of Armor (Gen 8): Challenge Beach, Fields of Honor, Forest of Focus, Max Lair, Soothing Wetlands
• Sword / Shield (Gen 8): Giant's Cap, Motostoke Riverbank
• Let's Go, Pikachu! / Let's Go, Eevee! (Gen 7): Saffron City
• Ultra Sun / Ultra Moon (Gen 7): Ultra Space

Raichu — full Pokédex entry