I seem to recall there being a fair number of them in Episode 1 (I forget the mission, but it's the Promethean one where you're in a competition to see who can clear their target the fastest).
Some of the Promethean target numbers (a few Covie ones, too) are just ridiculously high though. I feel like they kinda missed the balance between fun challenges to work towards while playing Spartan Ops, and mindless grinding. --- Is this finally a conundrum that CAN'T be solved by helicopter theft?
this isn't a perfect list, but it's prettty good. It shows best levels to get a lot of the commendations. It's what I've been using. Hope it helps! --- What can you do, when you live in a shoe, and you aint got no soul.