that's interesting to hear that. I bought my Shen Hao 5x12 not long after they first came out, very nice camera. I asked if they could make a 4x10 reducing back as well, they said no. So has the situation changed?
Are you a Chinese speaker? I always found it difficult to deal with them because of the language barrier. I'd get replies back that made no sense.
I will dig out my emails and forward my contact to you. Indeed there was a language barrier, but it wasn't too bad. I don't see why they wouldn't make the back up for you. But you could very easily buy the standard 4x10 back and slap it on a nice piece of wood...