Anyone at the match (preferably in the East stands near midfield) happen to take pictures (or even better, video) while Je-Vaughn Watson and Michael Harrington did whatever led to their red cards on Saturday? At the very least, did any fans happen to be looking at the incident while it happened?
It's really odd that none of the broadcast cameras caught the incident, and I'm not terribly optimistic that someone in the crowd happened to shoot a brief incident that occurred far from the action, but might as well take the shot in the dark.
Note: MLS almost surely has footage of this incident at their disposal. Every MLS stadium has panoramic video of everything that happens on the pitch at all times. It should be no problem for them to go to their footage from late in the first half, zoom in on Watson and Harrington, and judge whether the officials were justified in their supremely unusual ruling.
Best case, MLS will do just that and release the footage publicly. I'm not holding my breath, as the league is hardly known for its transparency, but at the least they could review it to see if the two players deserve to be suspended next week.