The model is also known as the "aluminum Deardorff". I don't have an 8x10 back for it.
I'd prefer to find one originally built for the camera, but could go with just about any 8x10 back that measures 11-3/4" square.
Interestingly, the 4x5 reducing back that came with it was made by Burke & James.
I'd prefer to be emailed any response to this, but will check back here to see if there are replies.