Selecting multiple authors,series etc. when sorting by popularity

I wish to copy all authors with only one book in my library and move them to another library

In the tag browser if I click on A[xxx] I get all the authors whose last names start with 'A'

If I sort by popularity I get all books no matter which group I click on
(1 - 1[100] for example)

I cannot seem to figure out a search expression either although the information must be available somehow.

Any ideas appreciated.

Helen