Meh. Stomping around in the Mega-D in Resistance might work, but I'm not sure if enemies beaten in the Mega-Ds even give rewards. As an alternative, find a fairly unpopulated instance of the Southwest Desert, go to the Atomic Wasteland, and hang out near the ginormous nuke in the center of it. Eventually, a bunch of irradiates will start worshipping the bomb, and they will keep respawning infinitely and rapidly until the nuke eventually blows.
If it's questionite hour, start AoEing like a madman. If you got maintained AoEs (snowstorm, rain of fire, avalanche, etc.) you can kill two or three dozen irradiates with each attack, if you place it well. In addition to all the questionite and resources, you'll also scoop up lots of lockboxes, PRIMUS recognition, and Irradiate costume parts.