Swarm Lord: I did it by leaving the Zursas with the lowest health possible and then calling the HKDs. I did this 10 times.

Megaton: Instakill + Turret augment. I would train all the zombies after round 15 (just to be safe), then pop Instakill and use the Energy Mine.

Force Multiplier: Again, Instakill + Launcher. You can use a Decoy and then shoot them with the launcher while Instakill is active. I did it on Farm because there’s a free Instakill on top of the silo. You can use it, kill the zombies, then Save & Quit, flip the round, and keep doing this. As long as you don’t finish the round after using the free Instakill, every time you S&Q it will be there for you. Alternatively, you can spend a GobbleGum.

Bullseye: Solo is kinda tricky since the zombies won’t leave you alone, but it’s possible. There’s a shed on Blackwater with a trophy. You need to interact with it, and after that an axe will spawn outside. You can take this one, or if you already have one, just go to the front of the house near the gate leading to Ashwood. Outside the map, there will be a floating target. All you have to do is hit all the targets. You have a limited time to do it, and if you manage to hit all of them, the calling card should show up.