If they are the same size as Vallejo's, you might try white card boxes, those used for Magic: the Gathering. I recently switched over to Vallejo, and found the 300-count boxes will hold 20 paint bottles if you cut off the box lids and store the paint bottles upright (or upside-down so you can see the color!) The 400-count boxes will hold 28 bottles. After that the bigger boxes won't hold even amounts of bottles, leaving a space which allows all the bottles to fall over. The 300-count boxes cost me a $1 each, and hold enough to sort by colors, all my blacks, whites and washes in a box, all the flesh tones and their washes in another, etc.