The first answer you stumble across is one of the most obvious: Ithilmar, the sky-silver of Ulthuan, found only in the occasional eruptions from the volcano of Vaul's Anvil in Caledor. Light as silk and hard as steel, it allows the lightest and most delicate of weapons to retain an edge throughout an entire battle, and for the swiftest and most graceful of warriors to be armoured without encumberment. It is often described as priceless, but that is because the ones doing the describing are the sort of adventurers and mercenaries who come away with that impression after finding themselves unable to acquire it at the local blacksmith. Pieces of it do circulate throughout the Empire, either sold through Marienburg, dug up from former Elven settlements, or acquired from unscrupulous traders who barter with the Norscans or the Fire Dwarves for their plunder, and though the price asked for them is always exorbitant, the price that Laurelorn would pay to acquire some more would be greater still, as the amount available to them has only dwindled since they were cut off from Ulthuan. This would require a huge amount of liquid capital to act upon and would likely draw a lot of attention as astronomic offers are made for various items within private collections, but would greatly enrich whoever is first to act upon the opportunity.