The trick for taint in a void(ish) world is to create it with a crucible. That and taint spread are disabled for some reason, making this method impossible.
The other alternative is to trap animals in small places, poison them so they only have one heart left, then vent flux gas into the small pen. They'll die from flux taint and become tainted animals. You could then kill them for the tainted items. You can also do this with creepers, which create a small area of taint when they explode.
Thanks for the suggestion. I had already tried soaking a sheep in a flux puddle for a few in-game days, but all they did was stare at me funny. I never considered suffocating them. Fortunately, the same experiment yielded slimes, which uncommonly drop tainted goo. 20 stacks of cobble in a crucible simultaneously was enough to start the process and a looting 3 sword and a half hour of watching got me enough goo to make 8 filters.
Still... This is a highly counterintuitive process, and my gut feeling is that this was not intended as part of the 'vision'. As the_j485 just pointed out: this isn't a skyblock pack, so it seems that skyblock-fu shouldn't be needed to progress. Maybe when the in-game documentation that's missing from the PhoenixCraft tab of the Thaum is finished, there will be a clearer path. *shrugs*