I'm shifting from the 16-35mm rig to a different lens setup and letting go of all of the gear specific to that lens. All of this gear is used.
$1200 -- Nauticam 230mm optical glass fisheye dome port #NA-18812. The plastic hood shows quite a bit of wear, but the glass is clean. Or, well, as clean as I can get it -- the dome surface attracts dust like a cat that's been rubbed on a shag carpet. Comes with neoprene cover (much newer than the port itself, I kept losing the covers...) and the case it comes in.
$450 -- Nauticam N100 to N120 35.5mm Port Adaptor II #NA-37305. Note that this is the one designed specifically for the NA-A7IV, different than the other N100-N120 adaptor. Moving parts function cleanly, lock/unlock and focus move smoothly. Condition is definitely pretty good, but not perfect.
$350 - Nauticam Extension Tube 60 with lock (for N120) #NA-21160. Condition is great; o-ring is clean, lock functions perfectly.
$200 -- Nauticam SE1635-Z Zoom Gear for Sony Vario-Tessar T FE 16-35mm F4 ZA OSS Lens #na-37145. Lived inside the housing, rarely saw daylight. Complete with the little rubber shims. Label is mysteriously worn.
$200 - Nauticam SE1635-F Focus Gear for Sony Vario-Tessar T FE 16-35mm F4 ZA OSS Lens #na-37146. Installed once, found to be too much of a hassle, and just left it off. Almost new.