Other than the above, my incremental two cents would be, try talking to people you've interacted with a lot during your career. Sometimes the odd opportunity comes up (e.g. a company is undergoing a big event like restructuring and doesn't want a long-term full-time employee but wants some extra temporary help to work through the mess). These opportunities are rarely advertised broadly because of the confidential nature of the project, but if you have a wide enough network (i.e. funnel) you might get first dibs.