How to unlock mosquito

And gun is only an option for this fly you are not forced to use it 🙂.

I believe that was a Tides of War reward - If you go into your company and look around in your vehicles menu might be able purchase it with CC - if it's still unavailable don't lose hope as it should show up again for purchase in the future. I remember reading that all rewards will start to show up in rotations similar to the special battle packs in BF1

If you go to the armoury, click on a plane and then Replace Plane Will get the option to buy the plane and its the same for any tank that you are missing  @szynond 

/Atic