Yeah, I got lucky when I found my DDE bit. The company no longer exists, or if they do, they don’t make it any more.
It’s great because it uses 1/8" shanked diamond inserts, which are $5-ish on AliExpress. I just have to use my Dremel and cut the shafts to length. The original inserts - that I could not get any more - had a small shoulder that held them in the holder, but when I couldn’t get any more with that little shoulder, I just put a 1/8" magnet inside to hold the diamond insert in place.
Here is a new diamond insert at the top.
One of the original diamond inserts, spring and tension screw.
And the diamond holder.
Here is the replacement diamond insert cut shorter than the original, so the magnet that holds it in place makes it the correct length.
Also, made it easy to swap inserts - just pull it out and pop in the new one - no need to have to take it out of the spindle.