Barak Varr to Erengrad is about five thousand miles by sea, which is something like Helsinki to Rome or London to Miami. And Erengrad has a fairly significant Elven presence. So Barak Varr is probably not the answer here. Considering how long ago the Fire Spire fell and how much the Colleges have come to prominence since then, you'd need some theoretical Dwarven Karak very close to Praag who would have had some need to preserve every insight into the nature of magic they could get for the past two centuries and no opportunity to trade those books away to the Colleges...
I didn't think that Vlag had anything left from the time before... but then there was mention of Kislevian nobles being surprised to discover that the vaults their ancestors had placed their treasures within had survived, so it's likely that their archives could have as well.
... huh, now I'm wondering if Boyar Kalashinivik had anything in there.