Filter Mailing List report for unsent mails
Since this is a one time issue (now that you've resolved with MailChimp), I would use that CSV to 're-import' those intended recipients with an Unknown status. The CSV should have email address as a field, so you can use that to match up your contacts.  See Importing Data and Importing Data - CiviCRM Wiki for reference.

When you import the contacts, use the Update or Fill option for "For Duplicate Contacts" option (and they should all match if your dedupe rule uses email address). In one of the last steps of the import, you can add them to a new group. Use that group as the recipients for your re-sent mailing.