Where can I find additional book themes for Aperture?

I've made a few books with Aperture, which I've enjoyed and which turned out very well. However, I'd like to find more book themes. (A current need is a theme that is better suited for an actual travel journal with more text.) I've spent a couple of hours on Google and poring over the Apple sites related to Aperture, to no avail. I'm sure =someone= offers new themes, free or not. Thanks in advance for any assistance!!