I think you could be a little more specific...
But anyway, play objective game modes, like Domination, HeadQuarters or Hardpoint, or play ground war.
The objecvtive game modes, doesn't matter the mode you are playing on, have predictable routes and/or fixed cap points, so you'll be garanteed to find a lot of people to get your DKs.
And ground war is also a good one, because there are a lot of people on each team, so there is a chance you might find a group of people passing down your SMAW sights, waiting to get killed.
Hope this helped
You won't make many friends with this method, but play chaos moshpit till you get Nuketown 2025 on Headquarters, wait till your team captures the HQ, chill out at the back of the map (behind the tiny little fence) and wait till you're the last alive and the enemy team are all there campturing the HQ and fire away.
The beginning of Raid map when everybody rushes middle. Alleyway of Overturn. That sniper building on the ocean side of the map... I can't recall EVER going into that building and 2-3 of my teammates want to join me... sniping on this game is like trying to play solitare, you will NEVER be alone.