Carradice used to sell the Bagman 2, which had the rack mount struts; they tended to flex and break when loaded up because all the tubing was Aluminium. Various people have rolled their own - pretty sure someone on here did it and documented it (maybe in the bike packing thread?).
Have been looking at bagman supports, and seen some images with extra struts going to rack mounts on the seatstays, any ideas where these are from?