The main RuneScape Wiki has an article on: Mithril Mace
The Old School RuneScape Wiki also has an article on Mithril Mace.

A Mithril Mace is the third-strongest mace in RuneScape Classic. It requires level 20 attack to wield, and can be purchased from Flynn's mace shop in Falador, or made from one mithril bar by players with level 52 smithing, yielding 50 smithing experience.

Bonuses

Dropped by

Monster Combat level Quantity Rarity
Ice Warrior 57 1 4Rare
Otherworldly being 66 1 4Rare

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