Best way to get a pair is to buy a half dozen and pick the pair out when it forms. Thats not really an option for you though.
Males have longer fins and brighter coloration, females appear more stout, with less coloration and no fin extentions. But sometimes you have a firemouth that you are 120% sure is male, until you see it laying eggs one day. So there are no sure ways to tell male from female, just educated guesses lol.
And if you get two males there might be a slight agression problem, just make sure they each have places to hide and all that. Divide up their territory.