Force Distribution on Charged Surfaces

Hi, I am trying to estimate the distribution of forces between a flat negatively-charged surface, and another flat positively-charged surface. These two surfaces are placed at some distance (2r) from each other – the problem is that the 2r-space in between is filled with negatively charged spheres (with r radii), that are placed side by side. Of course we know (or rather need to play with) the charge density on the flat, and spherical surfaces. I hope that someone figured out the mathematical formalism for this problem, and even translated into a Matlab code. I would greatly appreciate any help, with ideas, or pointing where to look deeper. Many thanks!