Where do you go in soul silver to evolve shaymin?

You don't evolve Shaymin in SoulSilver. Shaymin only has two forms: Land Forme and Sky Forme. You can switch between them in SoulSilver by using the Graceful Ribbon, which is found in the Flower Paradise in the post-game.

To use the Graceful Ribbon, you need to:

1. Complete the main story and defeat the Elite Four.

2. Go to the Flower Paradise, located south of Eterna City.

3. Talk to the person near the centre of the area, who will offer you the Graceful Ribbon.

4. Use the Graceful Ribbon on Shaymin in your party to switch it between forms.

Keep in mind that Shaymin is not found in SoulSilver, so you'll need to obtain it from another source, such as trading.