A Possible Solution

Nothing appears to be working. I can't believe I'm proposing this but I actually think we need to contact Quintin. Well, you should, as I doubt he'll speak to me. Perhaps you could convince him to part with the other half of the recipe? Last time I heard, he was staying in Drustvar near Arom's Stand. There's a lot of alchemists in those parts, but he shouldn't be too hard to find. Best not to tell him I sent you. He may not be as forthcoming with the recipe.