Because our famously decentralized Harvard does not have a unified listing of research opportunities, you will need to be resourceful in identifying opportunities that best meet your goals.
MBB lists dozens of positions each year, and the right-hand sidebar gives other ways to identify available positions.
When you speak with people as you think about research, always network - they may know about specific opportunities. And do not limit yourself to posted positions; if you know or find out about faculty members or laboratories that do research that interests you, contact them and ask if they have positions or could use a research assistant. Even if these faculty or labs who do not currently have openings may have them in the future, and they can let you know if there are any preparations you can make to be a strong applicant.