How can I find a scholarly monograph?
A scholarly monograph is another way of saying a book-length treatment of one (mono) topic by single author. This is to distinguish the type of publication from other scholarly works, such as an edited volume of essays by different authors, or a dissertation or a journal article.
So finding a scholarly monograph isn't as hard as you might think, although the searching for the keyword "monograph" wouldn't help.
Some tips to finding a scholarly monograph would be to make sure there is only one author, and often the publisher of the book is a clue. You might see if the book you are interested is published by a university press, such as "Indiana University Press," "Oxford University Press," "Princeton University Press" etc.
Those characteristics can help you determine if a book is a scholarly monograph. But the way you search for one is by the topic or subject in which you are interested. For example, let's say you need to find a monograph on a topic in American History from 1866 to the present. You can choose any major event or figure from US history since the end of the Civil War!
If we were to choose a topic like Herbert Hoover and the Great Depression, we would find this set of search results. then, after reviewing these and applying the above criteria, we could select monograph.
The library has a set of ebooks called American Decades that would also help you pick an era, event or person to search for.