Launched in 2005, Japanese Writers' House is an enterprise owned & managed by TranNet KK, a Tokyo-based literary agency and book translation company. Our goal is to become a key platform for editors, agents, and translators around the world, interested in finding out more about modern and contemporary Japanese culture and literature. Showcasing a variety of interesting works with international potential on behalf of Japanese publishers and authors, we are very proud to be associated with an extensive network of talents and companies, ranging from budding young writers to long-established publishers, such as Kawade Shobo Shinsha, a firm founded in 1886. One of a handful of Japanese agencies promoting Japanese works in English, Japanese Writers' House is passionate about introducing Japanese culture to the world.
To find something that hasn't been translated, you need to check what has been translated, and work by elimination.
Index Translationum is sponsored by the United Nations and covers a very broad spectrum of languages and subjects. It is not as good as searching the Japan Foundation database, but you should check here as well just in case.