Drawbridgep, a short while ago someone here posted the link for a small program called Grass3d. Well on that site they have a small free program called scatter for use in creating clones of objects and scattering them within a prescribed area. I personally have not tried the program but it sounds like its something that may come in handy for your project.

The primary use of Scatter is to clone objects and scatter the clones over a defined area and space. You can finetune the manner the objects get cloned and scattered such as variable size, orientation, and grouping. For example, if you have a few 3D models of ducks (in .obj format), you can use Scatter to create a colony of ducks. The outcome of Scatter is a .obj file that contains all the clones. You can then import that .obj file to most 3D applications for rendering.

Heres the description page:

Program Info

And heres the download page:

Download

And heres the home page, there are other free programs here:

Home Page

If you try it, let me know if its any good.