Casting your own figures is fine. Casting or asking about casting kits for the casting of GW figures even if that is not the primary intent is something we cannot even broach or discuss on this forum.
As Willmark said, as ‘Chaos Dwarfs’ are mentioned here we had to lock this. Chaos Dwarfs are copyright and IP protected, so we shouldn’t really be discussing casting of those models.
However, if the thread had been phrased ‘where can I buy a casting kit for making copies of evil dwarf models of my own creation, and for my own use’, I would have posted this link (seeing as you are in the US):