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Here's the description of what's allowed in Media Mail, according to the USPS website:
Media Mail™ Small and large packages and thick envelopes can be sent using Media Mail. Contents are limited to books, manuscripts, sound recordings, recorded videotapes, and computer-readable media (not blank). Informally called "Book Rate," Media Mail cannot contain advertising, except eligible books may contain incidental announcements of books. Media Mail is usually less expensive than Parcel Post.
So, sorry to say, I don't think calendars can go this way.