Riolu locations — where to catch

In Lumiose City (Legends: Z-A)

• Académie Étoile — Trade
• Bleu Sector 5 — Walk
• Magenta Sector 9 — Walk
• Rouge Sector 4 — Walk
• Vert Sector 8 — Walk

In Paldea (Scarlet & Violet)

• Poco Path — Walk
• South Province (Area Four) — Walk
• South Province (Area One) — Walk
• South Province (Area Two) — Walk

In Kitakami (Scarlet & Violet – The Teal Mask)

• Fellhorn Gorge — Walk
• Kitakami Road — Walk
• Kitakami Wilds — Walk
• Mossfell Confluence — Walk
• Reveler's Road — Walk
• Timeless Woods — Walk
• Wistful Fields — Walk

In Hisui (Legends: Arceus)

• Icebound Falls — Walk
• Snowfall Hot Spring — Walk

In Sinnoh (Diamond, Pearl & Platinum)

• Iron Island — Gift

In Johto & Kanto (HeartGold & SoulSilver)

• Johto Safari Zone — Walk

Other games (9)

• Brilliant Diamond / Shining Pearl (Gen 8): Iron Island, Riley
• Sword / Shield — The Isle of Armor (Gen 8): Roaring-Sea Caves
• Sword / Shield (Gen 8): Dusty Bowl, Giant's Cap, Giant's Seat, Hammerlocke Hills, North Lake Miloch, Rolling Fields, Stony Wilderness
• Ultra Sun / Ultra Moon (Gen 7): Poni Grove
• Sun / Moon (Gen 7): Poni Grove
• X / Y (Gen 6): Friend Safari, Kalos Route 22
• Black 2 / White 2 (Gen 5): Floccesy Ranch
• Black / White (Gen 5): Challengers Cave
• Diamond / Pearl / Platinum (Gen 4): Riley

Riolu — full Pokédex entry