Traineeships are awards from outside agencies usually administered by graduate programs. The traineeship may or may not involve experience outside of academic work. Other places to look are your undergraduate office of financial aid, your undergraduate department, etc. Also look for state scholarships, to your parents' companies for possible awards, and awards available to minorities, women, children of veterans and children whose parents are deceased. Check with community organizations such as Elks and Rotary.
Many students take on a job while in graduate school, but only as a last resort.
Work, even part-time, is difficult and exhausting with the kind of study schedule you are sure to have. Departments prefer your work be limited to the lab or research type. You may find your institution is willing to work very hard to help you find work directly related to your study if you must work at all.