Carradice Bagman 2 support.
How does the rack attach? I have a Ti bike and it is not fitted for racks. I can’t tell by the photo if the connection is a pressure fitting or a screw fitting.
You can use p-clamps to attach the support rods to the seatstays, or Carradice sells a separate clamp that mounts to the seatpost (which has threaded bosses for the rods).