Could not find full names. You may already know this:
Maj Duncan (as of May 1879) was in MG Crealock's 1st Div, in the Divisional Troops, commander of the Ammunition Column, unit strength 75;
Capt Alexander was in MG Newdigate's 2nd Div, in the Divisional Troops, commander of the Ammunition Column, unit strength 68.
Source: Narrative of the Field Operations Connected with the Zulu War of 1879, Prepared in the Intelligence Branch of the War Office
Does not look like they were in a position to gain mention in the dispatches.
Good luck in your search.
Leadership is the ability to rise above conventional wisdom.