[Arran]

Mike;
  Those sound a little different from the ones that I have encountered but I think that they secure the brackets down sort of like rivets, I don't know if they are reusable or not, or where you could get new ones. One possibility would be to replace them with those screws that don't have a screwdriver slot, not quite the same but they wouldn't look out of place. The pin inside each bracket just sort of fits into the slots in each end of the handle, I don't think that they could be removed from the brackets, so I think you won't have any option but to remove each bracket to replace the handle. I hope that I am wrong, and that someone has a better answer.
Regards
Arran