Are "Helios Ore Search, Arnor Spice Scavengers, and Xyology Expedition" the only available shipyard missions that grant you a trade resource (granting Helios Ore, Arnor Spice, and Aurorus Arboretum, respectively)?  I looked through all the tech trees briefly, but couldn't find any other technologies that unlock additional trade resource search missions.  Seems pretty arbitrary to limit missions to these three specific trade resources, no?  Makes me think I'm missing something.  I ask because in my current game I have unveiled about three quarters of the map (medium sized map), but haven't discovered any planets with Xanthium Deposits yet.  And I need Xanthium to build a Stellar Forge Improvement.  None of the other civilizations have Xanthium Deposits to trade.  I can pay 1,000 credits for a Xanthium Deposit from the galactic market, but the government I am currently using doesn't have access to the market.  Does anyone know if there are additional trade resource search missions I am missing from the tech tree?  Thanks!