These guys might be able to provide what you are asking for. I'm sure the're not cheap.
http://www.artglassproduction.com/CastGlass.htm
or
http://www.robertkaindl.com/CastCrystalFurniture.htm
or
http://image.made-in-china.com/2f0j0...-AZS-Block.jpg

Casting large pieces of glass is a very time consuming process. After the casting process, it takes weeks to cool, as if it cools too fast it will break.