you can get the nvg in sandbox but you have to reach day 47 in your story mode save and you will get an achievement which will unlock tons of things in your spawn menu including the nvg goggles
I believe it might be a slightly later day now as it's on the last day of story mode, which I think is day 49 or maybe 50, but it's the pre-alpha complete achievement if you already have it remember to tick the "show spoilers" in the spawn menu in the bottom right, you can see in potato's pic
you can get the nvg in sandbox but you have to reach day 47 in your story mode save and you will get an achievement which will unlock tons of things in your spawn menu including the nvg goggles