If it wasn’t a WordPress.com blog then wouldn’t the supportbothavekicked in? Ii’m not quite sure why the url is necessary in this case.
Most people tend to fit their theme to their subject matter by uploading appropriate header images or background images. Your best option is simply to browse through the available themes, find something you like, then customise it with a book-themed header.
If they are not a .COM site then referring them to the themes section here would be bad for them – the support bot is not 100% and I have seen many people with linked sites that are asking about their .ORG install – so I try and make sure they are really asking about a site that is on WordPress.COM –