Where to catch Sandslash

In Kitakami (Scarlet & Violet – The Teal Mask)

• Kitakami Wilds — Walk
• Oni Mountain — Walk
• Paradise Barrens — Walk
• Reveler's Road — Static Encounter

In Johto & Kanto (Gold, Silver & Crystal)

• Mt. Moon — Walk
• Route 26 — Walk
• Route 27 — Walk

In Kanto (Red, Blue & Yellow)

• Cerulean Cave — Walk
• Route 23 — Walk

Sandslash — full Pokédex entry