Steve's water spray idea would be fun to experiment with, even if just for giggles, but my first thought is similar to Brian's. Spray the surface with a close-knit pebbly surface, then knock it down with a firm, fine-grit pad, like a Micro Mesh 4000 pad. Get it close, then switch to 6000, get it where you want it with 8000, and finish it with 12,000. Then apply a dark green or black wash.
Just spit-balling here. Tons of variables, would not expect to get this right on the first try. Getting the right pebbly surface will be tricky. Not sure how, but a number of techniques to try. It will be difficult to get the pebbly surface suitably even to produce the right effect when sanded. Using a firm sanding pad or even a sanding block will be crucial to maintain the fine edge of each of the polished-off bumps, which will be necessary to achieve the desired effect. It would take a lot of work and experimentation, but I think that's how I would approach it.