Summary

I was not able to find a printable case, so I had to invest a few hours to create one (and learn a bit about tinkercad... ;) ).

I recalibrated my printer, and increased all models by Y 0.42% & X 0.27%
I hope this solves the size issue.

Instructions

The hole for the screws are to tight for M3 (I had not M2.5 at hand...), but it works after drilling with 3,5mm (although this probably breaks the thin pipes, but they are not needed anyway). And I had to cut the hexagonal holes for the screw nut with a knife...
I did not plan any holes for the microphone, but this wouldn´t be printable anyway, I guess.
The Wifi version has a little notch in the corner, which seems the easiest way to get the antenna cable from the bottom of the board to the top.
You would probably need to drill an additional 3.5mm hole in the case top for the antenna itself. I am not sure yet where exactly would be the best place... Suggestions are welcome!

Banana Pro Case