Here is a free rock model, with 3 total LOD's (? level of detail) you are allowed to use this in your project. (BTW: i sculpted this, it is NOT a 3D scan)
Why? Currently I have nothing much to do with any game projects so i decided to make a free rock asset. See it like santaclaus! :)
Enjoy!
[CC Attribution] I will allow you to tweak, remix or use this commercially.