Where can I find Dust Spirits?

Once your sim enters the national forest area. Have them turn to their right, and go all the way down to the river. They only appear at night, so you must do this when it's nighttime in the game. When you get to the river, there will be a fishing spot there. There's a little hill just to the left of that fishing spot. You will find the dust spirits there. Stay by the river, and have your sim follow it until they reach the waterfall. Just inside that small round clearing at the waterfall is another little hill. The hill will be on your left at the entrance to the waterfall clearing. The dust spirits will appear here as well. Stay on the waterfall side of the national forest area, and follow that wall away from the river, bypassing the community building. There's another little hill just about to where your sim can't go any further. The dust spirits will appear here as well. Note this, when hunting dust spirits. They will appear in a different spot each night. :)