It appears the headtube reducer is still available from Problem Solvers.
There was a particularly fun batch of bikes with lock out function. Well, the lockout mechanism would some times have already failed in the box waiting to be assembled. Other times while on the show room floor. It was a 100% rate of failure on this particular model. Not an "if" but "when" is it going to fail.
C-dale had gone for 100% lockout and it was more pressure than the mech could handle.

On the other hand, This past summer I met a fellow touring on a custom Ti frame built around a head shock (and rohloff hub). He
said he was using a Magura? or some other aftermarket insert. I'm sure long out of production now, but perhaps something to keep an eye out for. He claimed to have 10,000 miles on the set up and also claimed to only get about 1,500-2k miles racing XC on the original inserts.

Our local P.D. had headshock equipped bikes. When they all leaked out after some years of use, they thought it best to pump them full of fix-a-flat.

So, the take away from all this? They are a great conversation piece.