How do you catch a sandshrew in Pokemon Diamond?

If you want to find Sandshrew in Diamond, you need the GBA game LeafGreen. You can encounter Sandshrew in the Wayward Cave, when you've inserted LeafGreen in the GBA slot of your DS. The Sandshrews there will be either level 16 or 17 and you have a chance of 8% to encounter Sandshrew.