Crackdown 3: Campaign

In the boss mission Quist's Logistics Tower (Purple icon, New Pantheon area) I was able to get this, along with Killer Cure for a Pounding Headache & Fists of BOOM.

As you're ascending the tower there are a few spots where a group of 5 robots spawn for an easy ground pound or flying fist.

*Flying fist unlocked at Strength level 3. Hold B to charge up the attack.

The way I got this post game was to fast travel to the supply point in The Vision called "The Vision High Rise" it's also the only fast travel in this area. I initially tried this on the enemies that always spawn on the highway but lasers were attacking them there. If you're fast you can get it there. The spot I got this was on the same tower as the supply point I went 2 levels down and came in from that highway side I mentioned earlier. If you miss it you'll have to just reload your game and they'll be back. My game is 100% complete all locations.

Edit: top of the science center in central shade has all the enemies you need. It's actually better than the original location I mentioned. The very top has nothing but small enemies spawn on two sides using pea shooters. Just hang out, let a bunch spawn in, and do whatever achievements you need.