I could never find any kits here in the UK. Wembley loudspeaker is the biggest reconing company here and they said they could no longer get them, and all websites that sold them listed as sold out. If you could see if they have any that would be very helpful.
I am thinking along the same lines. I used to believe that it was JBL magic lost to time that produced these drivers. From speaking to a lot of people who have worked with these loud speakers for a long time I've come to the conclusion that it was just about specification, and if someone now can reproduce the parts to the correct spec there's no reason to think they would be worse quality.
Voice coils seem to be the most tricky, as I was told JBL wound all theirs in house, and most other soft parts were from external suppliers. I've been trying to track down the company that winds the coils sold online now, but so far have not managed to make contact. They must have the specifications for JBL coils, otherwise how could they remake them?
Now, how to check if these kits are the correct spec...I cannot find any info on JBLs parts, voice coil dimensions, cone assembly weight, etc etc. I'm sure that info is out there somewhere, and then we could compare it to these kits. I will keep asking until someone with that knowledge will share it. I would have thought there was a JBL technical document somewhere that had all the voice coil information, spider stiffness, cone weight and dimensions etc.
From looking at this sellers website though google translate, it does seem to be that they offer very high quality kits for a whole range of JBL products. They also produce a paragon replica, the Japanese go bonkers for their JBL, I have a feeling it will match the spec. But that feeling is clearly not good enough, I agree that I would have to get a kit and test it fully to see how it performs, so I think that is the path I will take.
The fact that this seller is in Japan, makes me think its much more likely to be the correct Hitachi cone. More likely than all the other kits available out there anyway. But until its tested fully we will never know!