I remember encouraging a certain sticky to be created to help in situations like yours.
Consider
referencing it, then, if needed, the
Immortal Contacts sticky. The sticky has not been updated recently, so you may need to do that.
From what I can tell, the MC has one leader and their patron, Achernar, has been declared slightly busy in other less... structured threads lately. You probably have a difficult chore ahead of you, but that is not to say it is impossible.
There is no clearinghouse for the identity of faction leaders because of the premise that some may wish to remain secret. Because of this, no one is obligated to help you find the leader of the MC if there is one, so being cordial may be of some use to you. I believe the recent leader's identity is known, as far as the Astral Boards are concerned.
E-mailing the appropriate immortal is your last line of action, and should be the end of your frustration on the issue.