Can only find these in the UK:
https://www.ebay.com/itm/285639613215?hash=item4281729b1f:g:1yUAAOSwfwlll~lY
https://www.ebay.com/itm/285639613215?hash=item4281729b1f:g:1yUAAOSwfwlll~lY
Maybe you could keep the boxes you like, put the working drivers in them, from the linked speakers. Then sell your current boxes for diy, since some people might build an active version with their own filter and any other KEF driver that they might get their hands on. Many people have a trouble building nice cabinets but have all the other ideas and ambitions.
I also believe that quite a few KEF drivers share the same cut out, if it's the mid woofer with bigger suspension, and not the dedicated midrange from the bigger R series
I also believe that quite a few KEF drivers share the same cut out, if it's the mid woofer with bigger suspension, and not the dedicated midrange from the bigger R series