Hi,
you need to manually bind and reference prefabs together, it's a common problem.
You do that, either by "searching" for them using the "findgameObject" action, but I don't recommand it.
you can also fire global events, when a prefab is instanciated for anyone interested to store its reference. for example "GEM INSTANCIATED" would be a global custom event, and any object will to keep track of gems would implement that event as a global event in their fsm and store the gameobject who sent that event, knowing it will be a gem.
then you can do all sorts of filterning, by tag, by name, or even access fsm in that sender, if you expect a certain standard. For example if all your gems MUST have an fsm called "Gem Interface", with some variable in there, you can safely access it blindly using "Get Fsm xxx" because only gem can send that event "GEM INSTANCIATED".
Does that make sense?
bye,
Jean