if you mean that when you can see it in the main menu of the game, you can't get them so soon, or so easily. but if you play the game with PC, you can use the console code to bring them in your inventory.
use this code:
armor : player.additem 129254 1 helmet : player.additem 145ec5 1
And, if you mean ranger patrol armor, it's not so hard to get them. The easiest way to get them is this. go to Novac and find Ranger Andy. kill him in any way and get them.
If you mean the veteran ranger outfit with the helmet and trenchcoat its located in the ncr safehouse that you must be idolized with the ncr to get the key to.