Plans: Dark Iron Mail

Source
This item can be found inside the Blacksmithing Plans in Blackrock Depths.

Locations:
 * In the Manufactory, on a bench.
 * In the Mold Foundry just prior to the Manufactory on a table behind some Fireguard Destroyers.
 * On the ground in the Mold Foundry
 * Near Golem Lord Argelmach

Some (but not all) database sites have reported them being found in Stratholme, but no location information was provided. (Also, there has been a report that the plans in Stratholme summon an elite skeleton. No such reports have been found for Blackrock Depths.)