plug-ins midi for: Cakewalk Sonar Producer X1

hello I wonder how I can learn how to create plug-ins midi for: Cakewalk Sonar Producer X1? I remember that I ever programmed, and I have no idea how this is done ... I'm a songwriter and working with MIDI and MIDI in need of improvement within Sonar. is there any company that sells custom midi plug-ins for: Cakewalk Sonar Producer X1? thanks