A good place to start is with the psychology departments in universities in cities you will be visiting. Faculty and their interests are often listed on these sites. You may wish to contact someone and ask about speaking with your group. You may know of researchers at universities based upon topic-related research literature you have read. Contact them and ask if they would speak with your group.
For site and museum visits, check their websites to see who takes care of group visits. Then contact that person. Talk with them about your group size, your goal for that site, costs, and group discounts. It may be necessary to set up a specific date and time to visit. Some places may be very informal and others may require you to complete forms and make payments before the visit.
For tours, contact the vendor by e-mail or telephone. These are usually available on the their websites. They may be able to offer services and discounts not listed on the websites.
Network with faculty who have done similar study abroad trips. They may have contacts you can use.