The Apollo MK II. Just as in today's society, i can see companies competing for defense contracts. There will be some fighters which never get sold. The Mig 28 from Top Gun is actually a Gruman (iirc) design called the F-20 Tigershark(not a military designation). This plane was based heavily on the F-5, had the landing gear of an F-16, and they practically stole the cockpit from an F/A-18. The moral of the story? It was and still is one hell of an aircraft, but is arguably the best fighter never sold. The United states and the rest of the world never purchsed any of em.
If there was an Apollo MK II, it lost out to the Ulysses in official GTVA military contract competition. However, mayhaps some small government within the GTVA ordered some. Something along the lines of a regional government.......they do have their own militaries. This would explain why they are scarce, but also why they exist.
Just a thought.