Where can you find a Tropius on Pokemon Diamond?

You can't find Tropius in Pokemon Diamond. Tropius is a Grass/Flying-type Pokemon that is exclusive to Pokemon Pearl and Platinum.

It is found in the following locations:

* Route 209: Rare encounter in tall grass.

* Route 210: Rare encounter in tall grass.

* Route 211: Rare encounter in tall grass.

* Valley Windworks: Rare encounter in tall grass.

If you want to catch a Tropius, you'll need to trade with someone who has Pokemon Pearl or Platinum.