Not sure what you are looking for or how just browse for books? Here is a basic guide to help find music theory related items in the Library of Congress Classification System!
ML -- Call Numbers for Literature on Music -- Highlights
MT -- Call Numbers for Music Instruction and Study -- Highlights
Looking for different analytical techniques or textbooks for review of different pedagogies? You can browse the shelves and find these if you know a bit about LCC's classification numbers for Music and Books on Music.
Books on music begin with ML (literature on music) or MT (musical instruction and study); scores begin with M.
The Library of Congress Classification System is divided into large subject areas which are called "classes." All classes--and subclasses--begin with one, two, or three letters followed by a number which represents more specific aspects of a subject.
Below is an outline showing the main classes in LCC: