I'm another player, Kurumor. I just asked once to Mayor. My Persuade was at 56. I didnt solved much quests and never visited Village of Thule. High Persuade is the key.
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Make Hartwin's little orphans happy by convincing the Mayor not to cancel the festival because of the flesh eating disease
I don't know if this is going to work for you or not, but I just kept asking he Mayor, and he finally gave in. Whenever I was in Eldfell I would pass by and ask.
In my quest walkthrough it happend after solving some of the other main quests that are connected to Village of Thule. After solving some of them I did the talking and it woked. Try yourself.
I enchanted an Eye of Lava to Persuade +35 and that did the trick just fine.
The reward leaves much to be desired though. Hartwin gives you 2 each of 4 different types of scrolls: Smite Foe Mage Curse Wild Paralyze Mass Drain Health Not even fame increase.