I've never played a Zero(nor am I aware of how much you receive from the book and/or limited by accessibility), but here are some methods I used in the past may help you get charm:
-Farm Zakum Helmets. Equip and fuse them after wearing by becoming an alchemist. -Whenever Nexon gives out free nx or has the weekly wardrobe stuff(They sometimes give charm out). -Wearing Monster Park Mustaches.