How do you know what's out there?
While that's an existential question, it's a valid one. For your assignment, you're supposed to look at three method books. The Allen Music Library has a representative, not comprehensive, collection of method books. Representative means that we have some examples, but certainly, not everything that's been published. How to find those?
What happens when I search for...
Um. Yeah. Let's try a targeted approach. I did the digging to find an example -- and here are the subject terms used to describe it-- assuming you're looking for something to use with elementary/early high school students
Let's try a library catalog search using Bands (Music) -- Instruction and study.
Let's use the left-hand information (limits or facets) to focus the search.