The Armor King Location & Guide - Kenshi
If you're looking for [Specialist] or [Masterwork] endgame armor in Kenshi there's no better place than the Armor King vendor. As his name suggests the Armor King is the premier vendor for armor in Kenshi. He has a large stock of armor all of which is typically [High] grade or better. You'll find him stocked with multiple [Specialist] and [Masterwork] armors too every single day and his shop is open 24/7.
You'll find the Armor King in Wend which is an area just east of Rebirth and just north of Okran's Pride. Basically, Wend is the river that runs from Floodlands down into Okran's Pride connecting the two zones. The Armor King is found in the center of Wend which means you'll have to swim up or down river to reach the building he is found in (pictured above). I've included a map location below incase you're still struggling to find him.
The Armor King carries every type of armor from Light or Heavy and has every slot available including shirts (and Hiver shirts). He also carries a wide selection of armor types. I believe I have seen him carry every single type of armor except Crab Armour which as far as I am aware you'll need to obtain from the Crab Raiders down south.