I propose spomething Russian, Italian, Japanese, or even French. The US, UK, and the Germans are already very well represented.
For aircraft, I'll propose one or more of the following:
Russian TU-2, DB-3, or Il-4 bombers.
Italian SM79-III and P108 bombers.
Japanese Ki-21 bomber.
French D520 fighter or MB175 bomber
For ground vehicles, I think the only current void is a legit tank destroyer, but unfortuneately the US and Germans were really the only countires to employ major numbers of standardized tank destroyers w/ open turrents and all three examples have an open turrent and easily damaged or destoyed via aircraft cannon fire:
US M10
US M18
German Marder III (limited turret traverse should be given [30d?])
As I have stated in other threads, allow the TD's gunner two sight postions. One in the normal gunsight mode and the other over the top of the turret scanning the battlefield for targets (with high zoom like gunsight).