Ninjon just did a vid on weathering pencils, and they look very matte:
https://www.youtube.com/watch?v=3Lq-dcsXMxA&pp=ygUHbmluam9uXA%3D%3D
Failing getting new expensive things, I would try some regular (Non-cheap crayola!) colored pencils and/ or some pastels if you want a very matte look. In classical painting, the term for a very light transition of gradation is called "Ombre" and is usually done with oil paints very close to each other- But airbrushing is an option.