Birnam Plate Gauntlets is crafted with Blacksmithing in Mabinogi (gauntlets). This page lists everything needed to make it, checked against the game as it exists today. The interactive planner lives in the Blacksmith Companion.
How to get the manual
The manual is rank 7 and survives 30 uses; every crafting attempt spends one use.
Lingering Darkness: shadow mission from the Tara board. Manual drops from the Elite reward chest. Take it from the Tara mission board; Elite needs an Elite Pass held by the party leader.
Lileas: Jousting Arena Manager in Tara. Trade Jousting Points at her shop for manuals. Spend Jousting Points at Lileas's shop by the Tara jousting arena, earned from matches there.
Materials
Expect about 7 attempts per finished item (15% average progress per attempt). Per-attempt materials are consumed on every attempt; finishing materials once per item.
Each attempt uses
5× Iron Ingot — refine from Iron Ore (common low-rank Refining output)
2× Fine Leather Strap — weaving rank 6 on a spinning wheel