Not an inlay. Talking about the actual hardware being a trunk. Like the cat pen someone made where the clip was the tale of a cat and the band that separates the two wood pieces had kats engraved in it.
In addition to the aforementioned inlay kit, Exoticblanks has an elephant-themed Rotocrylic blank. I've made a number of these in other patterns and they make a really nice looking pen. If you're only making a single barrel pen, the second blank blanks make great seam rippers or other projects.