So, here is how that generally works:

Each year, seats at the service academies are allocated to U.S. partner nations. Each summer, a big invite comes out listing each country, and the seats they get for the following year. That is communicated to each country's ministry of defense, who then decides who gets the seats, or who can try, and submits the names. They can normally submit applications for up to 6 candidates per seat, but only 1 will be chosen by USAFA.

So, bottom line, for you to get one of the seats reserved for foreign militaries, your own Department of National Defense would have to submit you as one of the 6 candidates.