While surfing the Internet, you may discover a generous artist willing to share his/her artwork for you to use in your own projects. To do this, you can follow one of the two methods mentioned earlier; that is, move the desired asset in a folder inside your content folder or import the file using the File | Import | Anime Studio Object method.
If you're looking for a good collection of files, check out www.ContentParadise.com. This is Smith Micro's own file and service exchange powered by community members; they bring many assets to the table for you to utilize. Keep in mind that some members may charge for their files.