I'm honestly impressed with the level of quality that Matthew of Torac Audio was able to achieve. According to his product page, the diameter is 88mm. I designed and 3D printed a couple of plates, one that goes on the backside of the driver which secures it to the cups, and another that goes on the front side that the pads attach to.
Glad to hear you were able to salvage the drivers! It would honestly be kind of cool if you could purchase just the drivers, but liability would certainly be a concern with those kinds of voltages. I can't imagine how much work it would be to write up a thorough enough release of liability form to purchase them for DIY use. I'll definitely have to look into Nectar Sound once the funds present themselves.