The .onebin files extension was developed by Microsoft for OneNote files associated to SharePoint 2003-2007.
You migrate one or several OneNotes, and you notice that the files with the .onebin extension do not migrate to the destination.
The .onebin files cannot be migrated due to a restriction with SharePoint 2003-2007.
You may be able to download the .onebin files manually with the OneNote tool, and copy them over manually. You can see this Microsoft TechNet forum for more information on this solution.