Here is a set of asteroids to use with the Cycles Render Engine. You can either use the asteroids that are available or make your own ; Follow the 3 essential steps, and change the settings of the modifiers and the textures to get different results...
https://www.youtube.com/watch?v=Ii9GH3w07mc&feature=youtu.be
Thank you ! with pleasure ; You will have to come back at a later date to see if any improvements have been made :)
Looks very realistic. Thanks for sharing it with us.