For quest
I was trying to not spoil them since they didn't mention which quest they were talking about, this is why I was asking for more details about what they wanted.
Also, if you are too accurate in your answer then you spoil the enjoyment to explore and find the solution themselves.
If they had confirmed that it was for the reconstruction of the barracks then I would have answered: "Sir Edward told you that someone in the capital might be able to sell you stone, right? Then talk to everyone in Aldlyn and you will eventually find what you look for. ;-)".
This way, I wouldn't have spoiled the enjoyment of discovery for them, I would have provided guidance but let them find the solution for themselves, save their enjoyment of discovery.