Here is a quick tutorial on how to create some very nice image based textures for Bryce. I am using Bryce 7 Pro but the same process can be used with older versions also.  With a little experimentation you will soon have your own metals and stone textures.

First search the web for free grunge images for use with Photoshop. There are tons of them out there.

I suggest you look for hi-res images. You can also use a 2D image editor or paint program to create even larger seamless tiles from the image.  Here are a couple tutorials on how to do this with Adobe Photoshop. You can find the same type tutorials for other applications on the web. Just remember the larger the image the more computer memory it will require.

Making seamless textures using Adobe PhotoShop

http://www.photoshoptextures.com/texture-tutorials/seamless-textures.htm

or

http://3ddojo.blogspot.com/2008/03/custom-made-seamless-texture-tutorial.html

Save those images to a folder you can easily find from Bryce.