If you want to try and figure the weight out yourself, go to Cedar Valley Roofing. There, you can figure out the weight for THEIR shingle and get an estimate as to your requested weight.
Or, you can go to Brother's Roofing and get a TON of links to roofing companies. Also, among the list is a link to the National Cedar Shingle And Shake Burear. For sure, they can be contacted for info.