Everyone knows that in Lonesome Road at the end of it you are rewarded a Courier Duster related to a faction.

(NCR) Bear: Lbs. +25, END +1
(Legion) Bull: AP +15, STR +1
(The Strip, House) Old World Flag Duster: Rad. Res. +30, AGL +1
(Independent) 21 Duster: LCK +1, Pois. Res. +30

What duster you get is determined by your reputation and nothing else. You could've killed everyone and it would still go by your reputation.

If you are idolized with all factions and you get NCR's then there is a reason for this.

NCR has top priority with the dialogue and duster.
Legion is second and the The Strip (House) is third.


If you want to get the independent duster then you need to have those factions at Wild Child (at the highest), it would still work if they are lower.

You can also use faction armor to get the independent duster since it resets faction rep.