There is another option at
www.eco-digital.com, it's somewhere in asia and the prices are in an asian currency, so I have no way of knowing if they are high, mid or low prices. Supposedly they have a sliding adaptor back that might fit on a Toyo, but I am not sure.
Tested the Phase Sliding back and the Kapture Group one. The Kapture seemed unuseable, from the point of view of focusing thru their groundglass. The magnifier that came with the unit was a pop-up Hasselbad one and it was like looking thru a bad peephole in a door. The other photographer that I was with got his Hasselbald pop-up viewer on and that worked a lot better. I could not honestly say that it worked well enough to be useable.
You must test these things. Also try ebay, you might get lucky and find a Phase Sliding Adaptor for a good price.
Brian