Here is more info about judo ball. It has own patent. Pdf with more info and description is here http://www.freepatentsonline.com/4998719.pdf
Before 20 years ago I watched some instructional film from Mr. Jahoda and his sons (both were Austrian judo national team members later). It was nice video.
Here is photo of Mr. Frantisek Jahoda from one seminar in Jicin, Czech Republic around year 1990.
More info about judoball ( selling / patent info etc. ) could have Mr. Jahoda Martin from Judoschule Sakura Salzburg Austria ( http://www.judoschule-sakura.at/kontakt.php )