Hi Thommyd
Dwarf in this case is a guest race, it is available from chapter 6, Fairy in chapter 7, and so on. Each of these chapters has quests that award diamonds.
The culture Wishing Well does give a few diamonds as well. It is prize from the last two or three large events, as weĺl as the award for finishing path 3 in the last Fellowship Adventure. It is 3x3, needs a path and expires in 100 days but it's output was recently improved. Maybe you have one in your Summonings bag