I wanted this bow so set about clearing everything in the zone, and ultimately got one (so it still drops). Here's what I learned:
- a rust covered model dropped it for me (not currently listed as a dropper)
- All three droppers (including a corroded prototype and a malfunctioning system) can be up at once, but there can only be a max of one of each named up at any one time. In other words you should kill each named as soon as you can so that it doesn't block the fresh one spawning.
- There are a large number of PHers, perhaps every mob outside of the factory.
- They spawn in the place of every mob type and every spawn location without noticeable descrimination
- They always seem to drop 1 wearable loot, along with the other zonewide trash
- I had drop: 1 ulak, 1 bow, 5 torques and 5 caps