Argentinians DO NOT LIKE CILANTRO. Argentinians prefer parsley as they are DESCENDED FROM THE BOATS, unlike the undifferentiated cilantro loving grubby Bolivian, Chilean, and Peruvian cholos.
You can, of course, find cilantro, mostly quite fresh, stored in a fridge, at the back of your neighbourhood veggie stand (mostly run by Bolivians anyway). Cilantro really needs to be fresh, as a dying cilantro stalk will desperately wrap itself around its healthy neighbour. Wrap in damp tissue to store at home in the fridge.
Peruvian restaurants are possibly the best CABA has to offer. Maybe you need cilantro and some dirt to make things taste good.
Don’t be a pushover. Don’t be tetchy (the sandwiches for people without teeth had me going for a while, but whatever). You can find most things here with a little persistence. When the going gets tough, the tough get going, right?