After some time searching, I finally found a box big enough for just 6 half-pans, and nothing else (or almost).
It's an old italian liquorices metallic box (the design is old, the box is new, and the liquorices really good!). It has just two little faults: the cover doesn't reach horizontality when opened, and the interior is golden coloured and so, it's not possible to mix colors. The first is not serious and after some use the cover gets some looseness and lets down with no problem. For the second, I fitted in a piece of white glossy rigid plastic that works really fine.
The actual size is like a classic Zippo lighter, less wide but slightly higher.
The loaded weight is 40 grams.