You can try checking at your local bookstores. They usually have a good selection of new novels, including ones like the new Gosick novel if it has been released widely.
Well, we can probably expect more of the unique mystery-solving adventures. The characters might face new and complex cases, just like in the previous parts of Gosick. Maybe new relationships will develop or old ones will be further explored.
GOSICK's anime, novel, and manga were related but not completely independent works.
GOSICK was an adaptation of the novel of the same name by Haihara Qiong, produced by Facebook. The novel was first published in 2011, and the animation began airing in July 2016. The animation mainly told the story of a detective revolving around various criminal activities.
GOSICK's novel was divided into two volumes, which told the story of the protagonist, Kuroshima Tomoya, working as a detective in GOSICK's office. Other than novels, there were also manga, games, and many other forms of derivative works.
GOSICK manga was a work published by Hachette, which was different from the novel. It mainly told the story of the heroine, Shirajima Reiko, as a detective, and Kurojima Tomoya as her assistant. In addition, the manga also contained some plots that had nothing to do with animation.
GOSICK W was a spin-off of GOSICK. It mainly told the story of the heroine, Reiko Shirajima, and her husband, Tomoya Kurojima, solving a case together. Unlike the original GOSICK, GOSICK W was more feminine in terms of story background and character setting, and it paid more attention to the description of the feelings between the characters.
The author of Gosick was JK Rowling. She published this novel in 1998. It tells the story of a lonely and mysterious girl who discovers something strange at school. As the story develops, she gradually uncovers a huge conspiracy involving history and myths from all over the world. This novel was hailed as a classic fantasy novel and was widely praised and sought after.