according to this, realistics aep are prohibited firearm (correct dimension and finish)
but one that would not look like realistic would not be consider a firearm
(so if you paint the airsoft pink it may or may not be consider a prohibited firearm at the discretion of the agent of the afsc who end up with it?)
and according to this
importing parts of prohibited firearm is prohibited.
so my guess was :
ok for battery and charger,
no for magazine (since they look like the real deal)
and a gearbox would be ''assessed on a case-by case basis''