I created the design in OpenSCAD, it didn't take very long, but I am quite familiar with this software. The .scad and .stl files are available from Thingiverse here: Ikea KVARNÃ lamp bottom and top cover.
I used some liquid nails to adhere the bottom cover to the lamp. The top cover just pops on. There was quite a bit of clean up I had to do with some fine files after printing, that's just a slight issue with my 3D printer though.
This is what it looks like without any covers...
Enjoy making your own!