There's also likely demand for resources only found in Coerthas. Both in mining and botany you'll find things like Jade, spruce lumber, Darksteel ore (rare), and as per mining leves "Blue Mythril". There's also an Ixali daily quest for miners to harvest "Furite", a key component to making the alloy known as Ishgardian Steel. Many many others, as well. =) I imagine in just Coerthas alone, there's a treasure trove of trade commodities for export that Gridania, a veritable 'bread basket' nation, would willingly trade their foodstuffs for.
