A good lathe could produce almost mirror surface with the proper cutter.. before hardening.
Hand sanding or placing the rods in the tumbler will render them unstable for "precision" work... but I suppose you already know that.

You need something to rotate the rods along its axis. The most efficient way I can think of is... chuck it in the lathe and use a tool-post grinder with a fine git wheel.

If you don't have a TPG you can use sandpaper and wrap the paper around the rod like a belt and traverse it up and down the rod as the lathe spins... not very accurate, but quick because the lather provides the power.
If you don't have a lathe then chuck it in the hand drill and use sandpaper.

If the rods are too big for the drill... then you have a problem.