The easiest farm for this I found is to go to a lower difficulty like Elite, and then in the first Act, find one of the Vaults that has an elite beetle. Your goal is to leave the elite beetle alive, and let him spawn his groups of mini beetles that he spawns 6 at a time. Use the kick to kill that group repeatedly. As long as you dodge the large beetle he will keep spawning the groups. A little time consuming and dull, but should get it done far faster than you would otherwise.
Also possible, although not always lining up as well, and more dangerous, with Corrupt Monks later on in act 3, who summon the exploding lanterns.