If you didn't complete the triumph during season 6, unfortunately the Service Revolver is unobtainable at the moment. [quote][b]Seasonal Weapon Drops[/b] After Season of the Drifter concludes on June 4, the following weapons will be unavailable to unlock at their respective vendors for a limited time. An issue was discovered late in development, and we are working on a fix for a future patch. Service Revolver from Commander Zavala Last Perdition from Lord Shaxx Players who have already unlocked these Year 2 variants will continue to receive them as random drops from rank up packages. Players who do not unlock these weapons by the June 4 deadline will be able to acquire the weapons once they are addressed in a future update. It’s worth noting that pursuit rewards such as The Recluse, Oxygen SR3, and 21% Delirium will continue to be available.[/quote] https://www.bungie.net/en/Explore/Detail/News/47833