I can recommend this book: https://rowman.com/ISBN/9781633886124/Alone-against-Hitler-Kurt-von-Schuschnigg's-Fight-to-Save-Austria-from-the-Nazis This book contains a lot of information on this topic and many sources. I can also recommend Kurt Schuschnigg's post-war books "Austrian Requiem" and "Brutal Takeover". And this study is about the Fatherland Front structure: https://epub.jku.at/obvulihs/download/pdf/379849?originalFilename=true