All supervisory positions are promotional only. They currently, and as far as I know, have never offered those titles to the public.
Assistant Train Dispatchers(ATD) promote from Conductor, Station Agent and Collecting Agent.
Train Dispatchers(TD) promote from Train Operator, Tower Operator and Assistant Train Dispatcher.
Console Train Dispatchers, the job in question, is not a civil service title. It's a resume-based position that only ATDs, TDs and Train Service Supervisors can apply for if they want to work at the Rail Control Center.