An easy, convenient way to farm Simaris standing is using Ivara in the Kuva Fortress exterminate mission (Dakata). Stay invisible the entire time and do stealth scans on all the enemies, turrets, cameras, etc. Scan, kill, repeat. You will generally reach the daily limit before even completing the required amount of kills for the mission.
● For the Ivara build, focus on Duration (225+), a bit of Efficiency (+/-150) and perhaps some Enemy Radar mods.
Alternative, you can use Loki or Octavia, but you’ll need to be a bit more careful with your energy / staying stealthy.