Marowak locations — where to catch

In Johto & Kanto (HeartGold & SoulSilver)

• Johto Safari Zone — Walk
• Rock Tunnel — Walk

In Kanto (FireRed & LeafGreen)

In Sevii Islands (FireRed & LeafGreen)

• Sevault Canyon — Walk

In Johto & Kanto (Gold, Silver & Crystal)

• Rock Tunnel — Walk
• Route 10 — Walk
• Route 9 — Walk

In Kanto (Red, Blue & Yellow)

• Cerulean Cave — Walk
• Safari Zone — Walk
• Victory Road — Walk

Other games (6)

• Sword / Shield — The Isle of Armor (Gen 8): Max Lair, Potbottom Desert
• Let's Go, Pikachu! / Let's Go, Eevee! (Gen 7): Fuchsia City
• Ultra Sun / Ultra Moon (Gen 7): Heahea Beach, Ultra Space
• X / Y (Gen 6): Friend Safari
• Black / White (Gen 5): Unova Route 15
• XD (Gen 3): Citadark Isle

Marowak — full Pokédex entry