I have had Jaheira in my party for over 3 months now and Im still waiting Elmister to show up with that Harper pin. I killed Dermin and when does Elmister shows up with that pin? Is there a bug in the game or do I have to do something else?

Hmm... I've had Jaheira in my party for 30 days while I did all of the quests in Athkatla, the whole Umar Hills area, Brynnlaw and Spellhold. In all that time her Harpers subquests wasn't even hinted at. When is it supposed to start anyway?
I dumped her in Spellhold for Imoen for the time being, but she said she'll be in the Harper HQ "if I can find them" when I get back.
Any ideas what's up with that?

Immediately when I finished the Montaron/ Xzar-quest, this harper girl appeared to call Jaheira to the Harpers Headquarter somewhere. She leaves the party for a day or so and returns to tell you to show up at the harpers building in the dock´s district.
There you finish off that ambitious harper´s boss there - Jaheira helps you and "traits" her harper friends.
After that I met some harpers in the druid´s forest and then in the temple forest, but because I play good I talked myself out of trouble.
However I don´t know how it goes on, because then I was sick of Jaheiras mourning about my good reputation so I kicked her off my party.

Hope I gave some help. Anyone knows how it goes on?