My tomatoes have been slowly developing black spots on the leaves for a while now. I cant figure out what is causing it. I also just found some tiny bugs all over the plant today, but I can’t figure out what they are either. I couldn’t get a very good picture of the bugs because they’re so small, but they are black with a yellow arrow shape on their backs. They aren’t very active, as far as I’ve seen they don’t move at all. Also, I am in Oregon if that helps.
First, I'd like to give you a big thumb's up for researching the insects you saw rather than just going "On no, Bugs!" and blasting them with the nearest pesticide. According to North Carolina State University, insidious flower bugs are a great control for thrips.
The damage to the leaves does look like it was done by thrips, so you could easily have made the condition much, much worse by killing off their predators! As it stands, the insidious flower bugs are probably your best defense against the thrips that you have, as they are difficult to eliminate with non-systemic pesticides. These pesticides also kill the insects that pollinate your tomatoes. Over time, the population of the insidious flower bugs should increase to match that of the thrips, and the leaf damage should stop as the thrips population decreases due to predation.
Much more information about thrips (written from a greenhouse production point of view, however). Based on this information, I think you may have Echinothrips americanus thrips.