There is currently only 9 citations styles visible in Fiduswriter. But Fiduswriter has a lot more - it has in fact all the 2267 citation styles that are currently in Zotero. It is almost certain that your particular citation style is also available in Zotero. There is a browseable list here: https://www.zotero.org/styles How do you get to these citation styles?
Create a document template. In the document template editor, only one citation styles can be assigned to the new template. The reason to limit the citation styles to nine is that Fiduswriter would have to open all 2267 Zotero citation styles simultaneously every time the user opens a document. So what you need to do is create a copy of the default document template and then choose the or those citation styles that you want to see in your document. The end user therefore needs to create her/his own document template together with the desired citation style(s).