I asked Tenyo about their available and discontinued product list.

Message: Is Prison Box and Magical Door still being made and sold? I see on your official list of products both are not marked as discontinued, yet I see sellers claim both these items are in fact discontinued. Can you verify for me if they are discontinued or not. If they are discontinued can you please update the discontinued items on it.

Response: Dear Richard,

Thank you for your mail.
We updated our products list today. You can see our discontinued items at present.

http://www.tenyo.co.jp/magic_en/alllist/right.html

Magical Door is still available but Prison Box is discontinued anymore.
*Please understand that available and discontinued items might be changed in future.

We hope you'll enjoy our products.

Sincerely,
Kenichi Komiya
Tenyo Co., Ltd.
On 2012/05/04