Okay I admit this wasn't today and I actually got this a couple weeks ago, but in the interests of topic change:
All three in Riverside Province, but that's my preferred area for mass murdering Mantle.
It's a little curious how I went ~30 weapons on the mesmer without seeing a mini and then come along with a necro and get three in the space of 10 weapons or so. Not that I'm complaining, of course! There's a bunch of differences just in WiK progression itself (mesmer has battle for LA available, necro did bare minimum to get to LA keep), and that the AP approach is anything from 30-100% faster than what I was doing on the mesmer, or it could of course just all be in the fickle RNG.
Since the mini peacekeeper is the only WiK enemy drop I haven't got yet I thought I should try to get it despite the fact I think he's ugly, and very rough numbers are making it look like maybe Peter Kadar's numbers for peacekeeper green drops might actually not be antifarm and they really are 3-4x suckier at dropping green weapons than Mantle. Plus it's not just one enemy profession that has no green to drop. Or maybe I'm now also antifarmed to heck. But, I'm getting about as many Mantle greens in areas which have 4-5x as many Peacekeepers as Mantle...? More data needed!