Okay, during Trials this weekend, I saw a couple pieces of Warlock gear that I've never seen before, and I'd love to know what these are and/or how to get them. And yes, I completely forgot to inspect the other players during our matches, so derp.

What's this helmet?

And what's this chest piece? This guy's the only person I've seen with it to-date.

Helmet is from the Lost Pacific set available on Titian.

Chest is from the Optimacy set available through Bright Engrams.

Source (with links to pictures): https://www.reddit.com/r/DestinyTheGame/comments/6zpmcn/all_current_armor_sets/

That was quick! :)

Not complete, but a good reference:

http://dulfy.net/2017/09/20/destiny-2-faction-vendor-armor-and-weapons/