Search bar

There isn’t a search specifically for reviews but you can use the regular WordPress search for reviews (or ISBN numbers) and get the results that way.

So there isn’t a specific shortcode for displaying a search box since you can just use the normal WordPress search, but I’m sure you could find a plugin that could give you a search box via a shortcode fairly easily.

For something that only searched the reviews, though, you’d need a custom search form that searched through book-review posts. If you’re interested in learning how that works (coding required), I have a blog post on the subject over on the WebDevStudios blog: http://webdevstudios.com/2014/11/04/hacking-wordpress-search-for-fun-and-profit/