Hmm.. After talk with Valena(?) I went to graveyard district in the night and she found me in a few seconds.
SPOILER
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I believe Harpers quest does not require Jaheira at all. (But I had her so I'm not sure).
First there will be a fight between areas within city and you will find a poisoned guy R... You have to take him to another guy R... in Docks (down the map left side). That moment an old "friend" Xzar apperars near inn in Docks. You have to help him to save Montaron from Harpers Hold - this is how it starts.
Need further tips - just tell.
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Well known expetitioner, Heffalumps hunter, friend of Boo.