Nikon has no obligation to supply parts to a manufacturer of non-authorized accessories. Don't make them out to be the bad guy.
If Katz-Eye wanted to make these screens, they would buy or borrow a camera to use to figure this out. Given the cost of the camera and their screens, it wouldn't be a huge expense. I believe this is what other manufacturers do.
Katz Eye hasn't produced screens for any completely new Nikon body since the D7000, and never tried to make one for the D3, 3s. Perhaps they are winding down their business.