I agree with gourami swami, North and Central American cichlids (like managunse and Amatitlania) are often much too aggressive for oscars, even a convict half the size of an oscar can shred its fins, and make its life miserable. And the cichlids GS suggests (being from S America) are much more geographically appropriate as tank mates, sharing a similar mild mannered temperament to the oscar.
They also share similar water parameters.
Central Americans come from much harder, alkaline waters than the South Americans, although oscars can usually tolerate these conditions, but often end up later in life, with hole in the head scars, to the bacteria more prominent in alkaline conditions, especially if a frequent heavy water change schedule is not adhered to.
Your tap water conditions may help in choosing stock, if your water is soft, with a low pH eg 7 or below), the South Americans are a shoe in for your tank.
If your tap water is hard, high pH 8+ then Central Americans could be a better consideration.
Firemouths also usually do better as a shoal of 4 or 5, as opposed to as a single individual.
Not saying it can't be done, but if you are hoping for natural behavior, and a copasetic group, you might just consider how things have evolved in nature.