If you have to be that particular to get the right shade of brown, you're better off shopping for the fabric locally, where you can actually see it. The biggest problem with shopping for fabric online is you have no way of knowing how true the colors in the pictures are. Your monitor may not be calibrated correctly, and the fabric thumbnails are sometimes photographed in weird lighting. I once purchased what looked like a soft, sage green fabric, only to find when it arrived that it was bright apple green.
There is one place I can think of that *might* work for you - Cherrywood fabrics. They are hand-dyed and come in color gradations. Maybe this would work for you:
http://www.cherrywoodfabrics.com/L_Image.asp?image=904
http://www.cherrywoodfabrics.com/8Step.asp