post boxes can be quite big, but also come in a variety of shapes and sizes.


And yes there are models on thingiverse: http://www.thingiverse.com/thing:1664844

To print a full size one would be a pretty serious undertaking, and unnecessary.

What i would do is find an existing cylinder: plastic barrel, oil barrel, huge cardboard tube etc.
And print the fiddly bits to glue on. And maybe make the big parts from paper mache or fibreglass or wood.