You can buy empty dvd cases, but the only place I found them without the hub thingy to hold a dvd is a wholesale place somewhere in the UK.
I know several ladies here looked for the "plain" cases like SU! sells and they couldn't find them either.
That said, I use dvd cases & just fit the stamps around the hub. I can get two sets in a standard size case and one in a slim case. These are "bare" rubber stamps.