You can get "Arcus Stones" by winning battles against certain Mamono in the following event maps or by mining in the map "Spot: B. Coalmine".

※You are able to check about Ice Axe and how to mine by clearing "Housing: Mining", which you can accept in main quest Ch.20.

Area	List of the Mamono【Arcus Stone】
[Adv] Spot: B. Coalmine	Zorumi
[Adv+] Spot: B. Coalmine	Zorumi
[Hell] Spot: B. Coalmine	Zorumi