Dick, I have not tried enough to find published accordion tutors in English presenting the said theories and methods from Hugo Herrmann and followers who have written in German. Here are some of the more significant publications however:
"Die neue Lehrweg für Akkordeon" Franz Krieg (Hohner 1949)
"Einführung in die Komposition für Akkordeon" Hugo Herrmann (1955)
"Tonbildung und Balgführung" Lech Puchnowski (Trossingen 1967)
"Balgführung und Tongestaltung" Puchnowski,Armin Fett (Wien 1968)
"Tonbildung und Artikulation auf dem Akkordeon" Nicolaas van Straten (Trossingen 1983)

If you want to find material in English I suggest you try asking Henry Doctorski for assistance first of all. Check his webpage, I haven't for a while, but you probably find fruitful links there.

I can shortly comment on some of the basics too later on if you like