hhsttb

Thank you :-)
None you can buy off the shelf (AFAIK) but a few frames share the post.
Was searching for a replacement for a while, after the my first frame was supplied with a post that was a bit too short. In the end I accidentally met another (shorter) PC owner and we swapped posts. Before meeting him I'd ordered a Fuji one from the US which looked similar (and had same clamp) but ended up tapering out to the same dims as a PX Stealth/Pro Carbon Track post, and I designed/printed off a 3D-printed plastic extension piece to glue onto my shorter one as a last resort (which almost certainly would have failed had I used it).
This probably won't be helpful, but below is a list of frames I've found (so far) to use the same seatpost moulding:

• Planet-X Stealth Track (the old aluminium one)
  
• Hed Aerolab V03 & V04 TT bikes
  
• Blue TR250 track bike
  
• (I'm sure there's one more but can't remember it. Will update if so!)
  
  

Also, I bought the frame (and swapped shorter post) from the guy I swapped posts with - incidentally the polished one in the photo is that frame, after I found a NOS uncut unicorn Hed V04 post at the January NCC Jumble for £5(!) so still have the shorter one spare if you need. If you're taller than 5'8", however, it's probably too short.