To get NVGs you'll have to swap out the helmet mounted display via ground crew option > change helmet mounted display. You either have the HMCS or the NVGs, not both at the same time. For NVGs make sure your canopy is open so they can give you the goggles. [?]
Toggle Googles RShift - H
Gain Googles Down RAlt - RShift - H
Gain Googles Up RCtrl - RShift - H
FlashLight LAlt + L