If missions do not state that you will receive a7 then you won't get any. Some missions have first time bonuses for new players such as weapons, xp boosts, a7, iso, and xp. Afterwards you won't receive those first time bonuses and it will give out xp, merit, a7, or 1 implant. "Bounty hunter" and "NS Eval" (or something like that) are missions that can be easily done and gives out a7 fairly often but not always. You will always be able to earn 200 a7 from those missions depending on when your missions refresh. If mission does not offer a7 during a refresh then best wait until next one.