Eventually, as this "school" of individuals passed away so to did knowledge of the system. This led to a lack of interest among most musicians and a dwindling of the materials over the years. The text, which spans to large volumes, started going out of print in the late 70's. Today only volume two is readily available. Two great artists of that period, George Gershwin, and Benny Goodman were both students of Schillinger. Gershwin composed "Porgy and Bess" utilizing Schillinger's method, as did Goodman when composing his "Moonlight Serenade".
I was introduced to Schillinger in the 90's while studying with Robert Doak. He gave me an article about the system describing how to utilize one of the techniques. The article showed step by step the creation of a rhythmic setting, and over-laying a pre-selected chord progression onto this setting. I was hooked. I hunted down the two volume set of books and eventually found both volumes in a book store in Wisconsin.
The two volumes each contain six of the twelve books comprising the system. Book 1 deals with rhythm, and becomes the basis for the remaining methods, described in the following books.
Lately there has been a rise in interest regarding the system. However, there remain to this day no true teachers of Schillinger's system. Schillinger trained several individuals during his lifetime with Richard Benda being the largest proponent of the system. Theses links show leaves advertising Benda as a teacher of the system; 1. 2. 3.
Having studied ,and utilized techniques of the system, I find it a misnomer that the system is a method of composing music, using math equations. The math is no more than a ruler for the music, placing abstract concepts into concrete, measurable concepts. However, there still has to be someone who understands the abstract concepts, and has the ability to write music. The system does not teach you how to compose, the system only provides tools and techniques which are utilized in the music you create.
For anyone interested in learning the system definitely consider purchasing both volumes. Used books occasionally show up on the internet and I've only found one place offering a reprint of the two volume set. The essential material is contained in volume one. Before purchasing, spend some time learning or brushing up on music theory as there is the presumption that you already know this material.