Leather Bandana 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 E and survives 30 uses; every crafting attempt spends one use.
Walter: Buy it from Walter's General Shop in Dunbarton. (1,250 gold). No special requirements, just gold.
Galvin: Buy a pattern from Galvin's shop under the Observatory in Emain Macha. (1,250 gold). None beyond having enough gold.
Effie: Buy tailoring manuals directly from Effie's shop at Qilla Base Camp in Port Qilla (1,250 gold). Standard gold purchase, no special currency needed
Pierrick: Buy it from Pierrick at the general store in Taillteann. (1,250 gold). Prices drop five percent on Wednesdays from the weekly shop discount.
Ilsa: Buy a pattern from Ilsa's general store in Tara. (1,250 gold). None beyond having enough gold.
Solea Chest: Open a treasure chest in the Solea caves using a Treasure Chest Key.. Requires a Treasure Chest Key, a rare drop from monsters in Solea.
Materials
Expect about 1 attempt per finished item (99.9% average progress per attempt). Per-attempt materials are consumed on every attempt; finishing materials once per item.
Each attempt uses
1× Cheap Fabric — Buy directly from any general goods NPC shop.
1× Common Leather — low-rank Weaving skill output
Finishing (once per item)
1× Common Finishing Thread — Buy directly from any general goods NPC shop.