New Rasputin bounties during the Season of the Worthy will send you on missions to find and kill powerful Cabal enemies. Finding these guys is actually quite easy, and our old friend Calus has prepared a nice buffet for us.
If you charge into the Leviathan, you'll find eight powerful Cabal enemies waiting for you, which are very easy to take down. Just shoot them or take them out with your weapon of choice. I like to just take out the first six, then reload the Raid again to make them respawn, and take out four more. You only need ten total to complete the bounty.
If you're not quite up to the first stage of Leviathan yet, public events are your friend.
The Cabal Excavation is a great place to find powerful Cabal enemies. You can find it at Artifact's Edge on Nessus and Lost Oasis on Io. Several powerful enemies will spawn during the event, so you should easily wrap up the bounty there.
The Injection Rig public event will also have a lot of powerful Cabal spawning. You can find this event at The Gulch and Sunken Isles on the EDZ, or the Cistern on Nessus.
If you play Gambit regularly, you can find powerful Cabals every time they become the enemy horde in this mode. It's not ideal, as you never know what type of enemy you'll be fighting, but if you're not in a rush and play a lot of Gambit anyway, it's a solid way to find them.