Your best bet is the legacy engrams, you still can only get vex or nechro from the old raids though, PoE guns also drop from the chest. I'm hoping for a special for the legacy this week, maybe I can get lucky for the 4th horseman.
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Fourth horseman also has a year 2 version. Xur could sell it or I got mine from a 3 of coins engram. Buddy also got one from the nightfall last week. Pretty much anywhere u can get a randomized secondary. Unless ur just trying to fill out your year 1 blueprints.
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I've gotten pretty much zilch from drops, 3 of coins works maybe every 12th time but ya if I could get the old one, then I can scrap it for a shard and buy the new one. It's the only year 1 exotic I don't have besides dregs promise and I'm on xbox so I only just recently got hawkmoon, and then got a legacy engram for monte carlo so I'd be happy to get a chance to try it out.