Yes, I already inferred that this country is involved in the conflict. And this country did plan on building their own engines, props, aircraft armament, etc (just not whole airframes in the case of imported aircraft). They did have a license, for example, to build the Merlin (which actually isn't unprecedented--the Czechs were trying to license the Merlin and Peregrine from R-R before the German occupation, per the Praga projects thread on secretprojects).
However, this country didn't want to just keep designing aircraft, and it was cheaper and simpler to import, and maybe license production. For instance, like Australia, who licensed the Mustang, Beaufighter and Mosquito at various points. Ideally, this country did have contemporary aircraft designed for late war, but as a contingency.
It's also an issue of standardization. They basically would want to standardize on the P-51H/L and P-82B (namely in cannon armed form) for single seat/single engine and twin engine fighter late in the war/post war prior to adopting jet aircraft. Of course, this is a real life pipe dream, but this is a "what if" topic.