Hi Martwansito,
Thanks for your reply and your link.
You are right, it seems they are many sizes of inlays for the Famicom Boxes.
But actually, I only need the standard size.
It's sad to see we are a few to search for those inlays.
Cardboard could be a good idea/alternative but I search for the original or good items.
But one more time: Thanks for your link