Where to catch Ekans

In Kitakami (Scarlet & Violet – The Teal Mask)

• Apple Hills — Walk
• Fellhorn Gorge — Walk
• Kitakami Road — Walk
• Loyalty Plaza — Walk
• Mossfell Confluence — Walk
• Oni Mountain — Walk
• Reveler's Road — Walk
• Wistful Fields — Walk

In Johto & Kanto (Gold, Silver & Crystal)

• Azalea Town — Headbutt, Walk
• Route 26 — Headbutt, Walk
• Route 27 — Headbutt, Walk
• Route 3 — Walk
• Route 32 — Walk, Headbutt
• Route 33 — Walk, Headbutt
• Route 4 — Walk
• Route 42 — Headbutt, Walk

In Kanto (Red, Blue & Yellow)

• Route 10 — Walk
• Route 11 — Walk
• Route 23 — Walk
• Route 4 — Walk
• Route 8 — Walk
• Route 9 — Walk

Ekans — full Pokédex entry