Without knowing any specifics about the nature of the mystery illness I'd advise starting with a general chronic illness support group and going from there.
Locally you can contact the nearest hospital for the day/time of a chronic illness support group. There may be listings in your newspaper. Your physician, or their receptionist, may know of other general patient support groups in your area where diagnosis isn't an issue or where diagnosis is
the issue. (You can ask around, I found a good arthritis group through my dental hygienist!)
For managed health care insurance problems in California: http://www.hmohelp.ca.gov/
The National Institutes of Health have an Office of Rare Diseases, including links to patient advocacy groups and research resources: http://rarediseases.info.nih.gov/
The Internet is always a great resource - as long as you let common sense be your guide.