I don't know if there is anything that is totally "canned". But I sent a few minutes using VS3D to come up with this:
I started with a rectangle, added a bevel, some random texture, and a few ridges and depressions. Once I had a rock finished, I stacked three of them and then did an automatic nesting (Allowing 180 degrees of rotation). So all the rocks in the wall are the same, but some are actually inverted. All in all, it took less than 10 minutes to build the surface.
I assume you are interested in carving concrete forms ?
VS3D home page: http://www.designscomputed.com/vs3d