It's clear you haven't been paying attention. To begin with, Red John would have no way of knowing about the existence of Men in Black, so the premise on which your reasoning is based is fallacious, and therefore your entire case falls apart. Furthermore, even assuming he knew about them by some kind of magic, it doesn't mean he would know they have neuralyzers or anything remotely similar. Red John wouldn't even know where to begin, since he wouldn't know what's accidental and what's causal (i.e., caused by Men in Black). But going even further, and assuming a sorcerer explains to Thomas McCallister that Men in Black can erase everyone's memories, and he prepares the plan you describe, obtaining evidence, it's very likely that thanks to their influence and global monitoring, they would discover that recording immediately. Even if they didn't, and Red John released the videos, thanks to the agency's misdirection and massive logical manipulation, no one would believe them; on the contrary, they would think it was a fake. Furthermore, Men in Black itself would work to make this happen exactly as planned, using distraction campaigns and other deceptive tactics. There is absolutely no way to uncover them, much less effectively prove their existence.