Light Leather Mail (F) is crafted with Tailoring in Mabinogi (armor). 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 8 and survives 30 uses; every crafting attempt spends one use.
Walter: Buy it from Walter's General Shop in Dunbarton. (16,000 gold). No special requirements, just gold.
Effie: Buy tailoring manuals directly from Effie's shop at Qilla Base Camp in Port Qilla (16,000 gold). Standard gold purchase, no special currency needed
Pierrick: Buy it from Pierrick at the general store in Taillteann. (16,000 gold). Prices drop five percent on Wednesdays from the weekly shop discount.
Sources that no longer exist: Beginner Gachapon (2012).
Materials
Expect about 3 attempts per finished item (40% average progress per attempt). Per-attempt materials are consumed on every attempt; finishing materials once per item.
Each attempt uses
1× Fine Leather — fragmentation of Fine Leather Strap (or weaving byproduct)
1× Fine Silk — weaving on a loom, low-mid rank
1× Common Leather Strap — weaving at a spinning wheel (or common low-level monster drops)
Finishing (once per item)
1× Fine Finishing Thread — Buy directly from any general goods NPC shop.