Tried and true homeopathic treatment for chronic persistent bad breath?

Need to be seen. You need to see a professional. Persistent bad breath is related to several health issues.
Determine cause. You can not treat halitosis until you determine the cause. For example, if cavities in your teeth or calculus deposits on your teeth or periodontal disease is the cause, there are no homeopathic treatments... You need to be treated by a dentist. Therefore, have exams with local dentist and physician to determine cause of your problem.