I have marked the places where I found my parts of the set. They may be other places, but it will always be one of the larger military locations (one in which there are at least two foreign supplies chests).
What ingot it will be depends on your level.
Raid civilian locations to gain crew rations and crafting materials.
Raid Military locations to gain foreign supplies, and crafting materials. Certain large military locations can also contain gear and weapons. If there is gear in the location then you will find it in one of the chests where there should be foreign supplies.
Raid Monasteries to gain books of knowledge, river map clues, foreign supplies, and crafting materials.
River Raid Basics
River Raids send Eivor and a crew of Jomsvikings to distant rivers at the Kingdom's edge and beyond in search of wealth and treasures of myth.
You can launch a river raid by talking to Vagn at the River Raid Dock in the Settlement. Pick a river from Vagn's map, hire a crew of trusty Jomsvikings, then set sail for the riches that await!
During a river raid, you will have to keep an eye on the health of your crew as you choose whether to continue deeper into the river to raid more locations or return to the settlement to bank your loot.
Different locations offer different riches. Civilian locations can replenish your rations. Military locations are rich in foreign supplies, with certain large military locations containing gear. Monasteries can contain foreign supplies, books of knowledge, and even clues to unlock new rivers to raid!
You can return to Ravensthorpe from a river raid at any time by entering the command position on your longship, opening the Quick Actions Wheel, and selecting Return to Settlement.
If your longship cargo hold is full, or if you and your crew are low on health and rations, it may be a good idea to return to Ravensthorpe to bank your loot, because if you die in a river raid, you will lose the loot you collected!
The River Raid Longship
Your River Raid Longship is a seaworthy vessel built for long voyages to foreign lands. When not raiding distant rivers, it can be found moored to the river raid dock in Ravensthorpe.
The longship is crewed by Jomsvikings, with Vagn at the helm, and your Jomsviking lieutenant at your side. You can assign Jomsvikings to your crew from among those you have recruited by talking to Vagn when setting off on a new river raid.
The look of your river raid longship can be customized using cosmetic parts you've collected. You can even copy the same look as the Drakkar.
You can also upgrade its cargo hold to increase the amount of Foreign Supplies you are able to collect and bring back from each river raid.
Raided locations
During a river raid, your Jomsvikings will burn down locations as they raid.
Locations that have been burned down will lie in ruins for several river raids, after which they will be rebuilt and can be raided again.
River Alert and Defenses
The smoke from locations you have raided will alert other locations deeper into the river. This is represented by the River Alert Gauge.
When the River Alert Gauge reaches the 50% and 100% thresholds, every location in the river will call in more enemy reinforcements, increasing the challenges you will face.
After completing a river raid, the higher you pushed the River Alert Gauge, the more River Defenses you will encounter the next time you raid that river - barricades, river chains, and enemy ambushes.
Downed Jomsvikings
During a river raid, make sure to frequently check the health of your crew.
If a crew member runs out of health and rations, they will enter a down but not out state, with a limited time for you to revive them - if you have a ration to spare.
Take care of your crew, because any Jomsvikings who are not revived in time will be out of action for several river raids.
