Where are the monster truck parts in mater-national?

Answer 1

Tires are behind the courthouse (Red's place in the movie); the statue of Stanley is in front. The horn is lying in the street in front of the Casa della Tires. The last piece is on the dirt track that's to the west of the big radiator-cap rock out in the desert.

Answer 2

there's one behind town hall, one mostly in front of you when you start trying to find them and one in the ditch.