Mongo's Traveler Suit (F) is crafted with Tailoring in Mabinogi (clothes). 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.
Nora: Buy it from Nora at the inn in Tir Chonaill. (1,250 gold). No special requirement, just enough gold.
Galvin: Buy a pattern from Galvin's shop under the Observatory in Emain Macha. (1,250 gold). None beyond having enough gold.
Ilsa: Buy a pattern from Ilsa's general store in Tara. (1,250 gold). None beyond having enough gold.
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.
Prairie Dragon: Defeat the Prairie Dragon that spawns northeast of Maiz Prairie in Rano.. Spawns only in two daily windows, mid afternoon and early evening, and can be fought as an open field raid.
Sources that no longer exist: Beginner Gachapon (2012).
Materials
Expect about 4 attempts per finished item (30% average progress per attempt). Per-attempt materials are consumed on every attempt; finishing materials once per item.
Each attempt uses
1× Cheap Silk — Mobilizing the Expeditionary Force shadow mission reward
1× Thin Thread Ball — Hot-Air Ballooning reward (6-10 stars) or gift from Simon
Finishing (once per item)
1× Common Finishing Thread — Buy directly from any general goods NPC shop.