Help Me Find BS Singularity SB!!!

Seriously... I've burned Atziri knows how many alts/augs trying to get singularity affix on a strongbox. WTF? It's the last one I need and I can't freaking find it. Of course, I haven't found a unique in about 50 hours of gameplay either so [insert RNG rant here].

Is the singularity affix map only? Is it level limited? Is it tied to only specific types of strongboxes? Is there a good area to farm strongboxes? I'm completely out of alts/augs now and I'm farming to get more but man is this frustrating.

I have found 3 or 4 singularity fixes. Pretty sure first I found was in normal, definitely wasnt merciless, I know none of them have been in maps. I had the hardest time finding the all linked one. I know only one of the fixes was on a magic box, the others where on rare boxes. But using chaos orbs to try and get fix is spendy im sure.

Took a while to get unity (all linked) and that was my second to last one. Since I've been only trying to singularity I've gotten like 6 or 7 unity. RNG rant rant RNG rant rant.

Thanks for the info though. Good to know I don't have to run maps or grind merc to find one. Guess I'll just keep plugging away.