HI, i have found that filco have made a palm rest that is made of natural stone. It's that possible get it in usa?
http://www.diatec.co.jp/shop/det.php?prod_c=1305
With the price of shipping rocks across the Pacific, I'd think it would be cheaper to visit your local granite countertop company and have them cut one to your specifications. They frequently have off-cuts and smaller pieces that are discounted heavily.
The only other expense would be the rubber feet, I use ones from Home Depot for my aluminum military keyboard, was able to find just the right size I needed.