I'm in my early 30s, and I recently had my maxilla and mandible non-surgically expanded with a combination of appliances, one called Advanced Lightwire Functional (ALF) and the other called Fixed Anterior Growth Guidance Appliance (FAGGA).
Treatments that make use of the Orthotropics philosophy or of appliances like the ALF or FAGGA are relatively new and are not mainstream. However, there are many case studies available online showing them in action and showing before/after pictures.
I don't know what kind of resources you're looking for, but this video [1] provides a quick introduction to Orthotropics.