Just stop by Home Depot or Lowes, etc, buy a duplicate size mild steel rod from hardware and run a power hand grinder down it in a straight line to grove it
If you do no know how to use a grinder or have access to a Machinist mill, ask your local high school or collage machine shop teacher to do it for a few bucks.
Of course, you could just pay a machine shop to do it for you and apply whatever finish you like, yourself.
Yes, brass and quality aluminum rods should work, but what ever length you settle on, make two, for for sale or as a spare.
IMO