A content instance that implements EPiServer.Core.IResourceable stores related assets in an instance of EPiServer.Core.ContentAssetFolder. Resources stored as content assets are considered exclusive assets for that content instance; you cannot select them from other content instances.

The following example shows how to get an existing assets folder or create one automatically:

contentAssetHelper = ServiceLocator.Current.GetInstance<ContentAssetHelper>();
var contentAssetFolder = contentAssetHelper.GetOrCreateAssetFolder(myContentLink);