Volume Beret is crafted with Tailoring in Mabinogi (hat). This page lists everything needed to make it, checked against the game as it exists today. The interactive planner lives in the Tailoring Companion.
How to get the sewing pattern
The sewing pattern is rank 9 and survives 30 uses; every crafting attempt spends one use.
Giant Headless: Defeat Giant Headless monsters in the Coill dungeon.. None beyond clearing the dungeon encounter.
Nightmare Humanoid: Defeat the Nightmare Humanoid boss inside the Albey Red Gem Dungeon.. Requires a Red Gem Dungeon pass to enter Albey Red.
Argus: Hunt Argus in Fiodh Intermediate, Fiodh Advanced, or the Generation 3 storyline area. No special pass needed, just access to those hunting grounds
Materials
Expect about 2 attempts per finished item (50% average progress per attempt). Per-attempt materials are consumed on every attempt; finishing materials once per item.
Each attempt uses
2× Finest Silk — weaving on a loom, higher rank
1× Fine Leather — fragmentation of Fine Leather Strap (or weaving byproduct)
3× Braid — low-rank Weaving skill output
Finishing (once per item)
1× Finest Finishing Thread — Buy directly from any general goods NPC shop.