I found this page which gives a lot of answers that lead me to conclude this is not a technique that can be readily adapted to DIY; considering you first need to make a very precise steel mold and the material cannot be worked after casting.
But the materials are not difficult to find:
"ZaniteŽ polymer composite is a blend of pure silicon dioxide ceramic (99.8%) quartz aggregate, specially formulated high strength epoxy resin and selected additives. The natural elliptical shape of quartz is ideal for casting intricate structures."
In fewer words; sand and epoxy.