The other 4 dwarf kingdoms
 

In the silmarillion, it speaks of the seven fathers of the dwarves, and says they go out and establish a seperate kingdom each. But the only kingdoms we hear about are Nogrod, Belegost, And Khazad-dum. Where are the others? Were they assimulated into the larger ones? I have no idea.

The stories only give accounts of events that occur in the northwest of Middle Earth. Maybe the other dwarf kingdoms were further east and south. In Unfinished Tales, one of Túrin's men does make this comment:

Maybe he was referring to Nogrod or Belegost, because they were also in the east.