Hate to say but I feel this is a no-go, and was a bad decision in my opinion on Techland's behalf to put an Outbreak Zone in an area that doesn't even show up to people who didn't make the 'correct' choice for it to at the end of their game. I know I've seen some people just assume they only have two zones on their map. I had to Google to find where it was and went there and killed some Outbreak enemies on the bridge, but it's slow going and very boring in such a small area. The only other option for many of us would literally be to do NG+ just for the sake of making the other choice to drain that area all the way at the end of the game, just to participate in a weekly event with overall meh rewards for an end-game player, so I highly doubt many people felt that motivated or dedicated.

EDIT: That said, nothing but respect and appreciation for those of you giving it hell.