Back in the days when KGB Consulting still existed, the phone calls would start around this time of year... people wanting a KGB Consulting pop-up tetradecagon calendar. (If the business had had as many customers as persons requesting calendars -sigh- but I digress.)
No, I'm not bringing them back; but now you can roll your own. Just go here and follow the instructions.
The site refers to the calendar shape as a "pentagon dodecahedron", but Stan Kelly-Bootle agrees with my nomenclature, since it's a 14-sided polygon, albeit three-dimensional.
Think of it as physical therapy. If you print it out on card stock and paste a rubber band inside, you can pretty closely emulate the pop-up quality of the originals.