Magic School Uniform (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 A and survives 30 uses; every crafting attempt spends one use.
Nora: Buy it from Nora at the inn in Tir Chonaill. (11,500 gold). No special requirement, just enough gold.
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: Production Gachapon.
Materials
Expect about 2 attempts per finished item (70% average progress per attempt). Per-attempt materials are consumed on every attempt; finishing materials once per item.
Each attempt uses
2× Finest Fabric — weaving on a loom, higher rank
1× Common Silk — buy from Seal Merchant (Mondays) for seals, or weave rank F
Finishing (once per item)
1× Fine Finishing Thread — Buy directly from any general goods NPC shop.