Some players in your position have reported that they have been able to obtain the new Exotic from the vendor by joining a Fireteam with another player that has claimed the Triumph and having them load an instance of Kepler. If that doesn’t work you should be able to get one while playing the Sieve Activity on Kepler, in which there is a period of “bonus time” after you defeat the boss of a given round. During this bonus time you will need to defeat enemies, grab the Motes they drop and bank them at the central platform to build up a meter. Completely filling the meter (which isn’t particularly difficult) within the allotted time will spawn three chests, one of which is quite large. From my experience the large chest seems to be a guaranteed drop of the new Exotic for your Class, provided you have claimed the required Triumph. (΄◉◞౪◟◉｀)