The Heroic Deed: Gun Wrecker requires you to Destroy 100 Stationary Cannons or Heavy Flammers, heavy weapon emplacements, as an Assassin.  They seem to only spawn on Tainted and normal Rebel Guard missions. They seem to also spawn more frequently on "Starship" maps which are scarce and never on the open "Deathworld"  maps which are very abundant on Assassination, Hunt, Siege, mission type.

I have 41/100 after playing on average 6 hrs per day over the last 2 weeks trying to clear all Heroic Deeds and the Halfassin is my only class with b.s. mission spawns.

Is there, by chance, a specific mission combo to guarantee Heavy Weapon Emplacements?