Gentlemen of America would keep the Gentlemen naming scheme. Maybe United Gentlemen of America
I agree with wanting to the keep the 'Gentlemen' in there: it denotes distinction and respect to the modders, and is simply consistent.
Presidents of Steelport? Nah. For one, President(s) refers to the ingame character; and outside the game, the idea of having multple Presidents, even as honorary title, is just confusing, as President is ever only the highest rank, and there's ever only 1 of them (per coherent community, as it were).
Also, 'Steelport' was meant to distinguish SR3 from Gentlemen of the Row (SR2). So, not twice 'Steelport', either, please.
So, after my long-winded intro, here's my humble suggestion:
Gentlemen of 'Merica
(Spelled SR IV style, of course, after the 'Merica gun)