I think your best bet would be the contact Toshiba about your problem. Perhaps they can tell you why TU56 failed, and if it's necessary to revert, they could provide you with TU31. Someone else requested TU31 on another forum back in Feburary and didn't seem to get anywhere (link), so I don't think that anyone except for Toshiba has TU31.
BTW, are you sure you want your e-mail address out in the open? The Internet is crawling with automated spam-harvesting robots, and they love to visit forums... PM me if you want your e-mail address removed from your post.