Weathering with chalks/ pastels?

You can get them at any artists supply/ craft store. I got mine at Michaels Arts and Crafts.

To use them, I sand off the tip until I have a pretty good sized pile of chalk dust. Make sure you sand them either on sand paper, or above a piece of regular paper. Then I fold the paper and pour the powder into a bottle cap. The I apply with a brush making only perpendicular strokes to the ground. There are anumber of ways to do all of this stuff, thats just how I do mine.

You can also try Weathering pigments like
www.migproductions.com

I just found this link, it is very good, I have to get some of these

http://www.missing-lynx.com/rare_world/rw05.htm

There are a variety of household items that can be used just like the pastel chalks. If you soak a piece of steel wool in water and then let it dry, you can get a fine rust powder from it. Plain old cement is a great weathering pigment and foot powder or fine white talc also works. If you want other colors, use your imagination or head to your local art supply shop and follow the advice previously posted.

I purchased pastels from Micro-Mark (Docs Brand), Hobby Lobby and Michaels. Be sure that you DON'T get the oil based pastels, as these won't work for the weathering you want to do.