Where can I get a box like this?

At Amazon. There’s everything. Enter “ Storage box small”.

Or you’ll get the flea market. For my power bank, I didn’t even have Amazon ne case in the right size… on the flea market I didn’t push a bit and then found a padded bottle case in the absolutely correct size for 50 cents.

Or, you’re making such a thick cardboard yourself… a children’s game…