The only way to do this is to grant reviewer permissions at the top mailbox level, then add them to the permissions to the additional calendar. Then the person to whom you have given permissions will have to add your mailbox to their folder list in order to see the calendar. Unfortunately when you try file, open, other users folder, and select calendar for that user you will only get the default calendar and no other options.

The only way to do this is to grant reviewer permissions at the top mailbox level, then add them to the permissions to the additional calendar. Then the person to whom you have given permissions will have to add your mailbox to their folder list in order to see the calendar. Unfortunately when you try file, open, other users folder, and select calendar for that user you will only get the default calendar and no other options.