These are the lightest IME
http://www.mpistocks.com/availablestocks.htm
I submit that "quality" has more to do with the gunsmith than with the stock blank. MPI's are well expressed, single layer fiber (4oz?) with a very light filler. The few MPI's I worked with were definitely not 'bolt ins' but were made into fine pieces. If you feel, as I do, that stiffness is important then you'll need a bunch of added interior gusseting which will add some weight. But this is another can a' stuff entire.....
You did said light
al