This is fairly easy to obtain in the first Boss area with the Spider.
First, kill the boss, but leave the spider spawn vents alone. I had the Micro Missile and Nanoedge Chameleon Skin equipped.
Each vent spawns 5 spiders, top left has 2 vents so you can easily gather 10 spiders right on you and fire. This may take a couple times, I killed 7 a few times in a row before the 8 happened.
Think this is the easiest spot to get it, because it's the same level setup each time.