How can I find a job if I have a mental illness?

With treatment. Depending on the severity of course. However, people with mental illness are able to find a job if staying compliant with treatment (medication as well as psychotherapy). Medication is needed to help you control whatever sx you're having. Psychotherapy will help you cope with job-related stress and build up symptom awareness to prevent relapse and any other issue that might arise in the process.
MENTAL ILLNESS. Some persons with mental illness if controlled by medications can find a job. They go to their primary md and psychiatrist together.
Job & mental illness. There are many kinds of mental illnesses, and none automatically precludes having a job. As a psychiatrist i've treated many people who have been able to work during their illnesses, depending on symptom severity. Please work with your psychiatrist on this, and don't sell yourself short! also listen to elyn saks speak about this: http://www.Ted.Com/talks/elyn_saks_seeing_mental_illness.Html.