The achievement is way easier and less luck based then it sounds.
While the spawn time of the hero tokens is random, the locations
do not change (at least on the new maps).
The quickest way for me was to play sabotage on Administrators Palace. As mentioned in the other guide back out if you start as imperial. On this map the rebels get 4 hero token spawns at the beginning before all generators are destroyed. Each token spawns on one of the four possible locations.
When the round starts just run to one of the spots and camp there until you get the token. I used the first location shown in the video and was able to get a hero in each round.
The tokens only spawn once per location so the rebels get exactly 4 heroes per round.
Thx to RivaThames:
The video is not 100% accurate on the spawns but once you have seen the token in game you know exactly where to camp.