I know Constantine has a place where he stores all kinds of dangerous artifacts and what have you, but I don't know if his little cabin of magical horrors is in Gotham, or if it can move around or if it can be teleported to though.  That's Ace's domain, so I'd ask him, but I imagine it has quite a few books from all over the world, so chances are that's a good place as any really.  That's not a bad idea though.  ;D