Fastest way to do this is to load up a custom escape map (Escape > Map sharing > 100k Farm > Host with this map) I made the custom map "100K Farm" ID: SCHF51. It's 12 bays of 200 Juvies each. each room has 4 salvos in it.
You need to kill enemies in Paduk's Fear Ultimate. Executing enemies get your Ultimate back faster and will send out a pulse of fear so use this on the Drones. There are plenty of explosive ammo boxes that give you flashes when u get them.
This is the card setup I used (notice my Paduk is pretty low level and still didn't take much time):
gonna leave my previous solution in case TC decides to patch custom maps