SpriteCollection and IconCollection - hippogamesunity/HeroEditorHub GitHub Wiki
You can find SpriteCollection and IconCollection in Resources.
These collections are initialized automatically on the app start, so you can access them via SpriteCollection.Instances and IconCollection.Instances (they are dictionaries with keys like "FantasyHeroes", "MilitaryHeroes" and other).
Each item inside SpriteCollection and IconCollection has unique Id that has the following format: {edition}.{collection}.{type}.{name} (for example, "FantasyHeroes.Basic.MeleeWeapon2H.BlackHammer"). Use this unique Id to find sprites and icons (you can make such property in your item class).