Thank you for coming to the community with your question! It's possible to view a count of how many people have unsubscribed year-to-date, but I'm afraid that there is not an export for those contacts specifically. I can absolutely add you to the feature request to have an 'unsubscribe date' option when exporting contacts. To see how many contacts were unsubscribed at least, you go to the contacts page within Constant Contact, and then click the 'Reports' sub-tab near the top of the page. Then you can change the time frame from the past 30 days, to the Year to Date option to view all the growth and unsubscribe numbers so far this year.
Thank you for sharing your feedback on this feature here in the Community as well! We have submitted this request to the appropriate teams. Please let us know if there is anything else we can assist with in the meantime.