i found it, i reckon you have to be sandy, the girl character to get it!
so what you do you try to get a game as sandy, also i think this has to be solo, i did it on solo. so what you need to do is not to kill any zombies, stay on round 1, go to the power station and turn on the power. after that you'll have to keep roaming around the map until the avogrado spawns, you have to do this on round 1 i believe. when he spawns you have to make sure you're at the bus depot, there you will kill him, after that, he drops another navcard, make sure you had money in the bank for jug before ya killed him, the card is full of electricity and zaps you to red health when you have jug on, if you are not sandy though it will kill you, sandy has some gloves on that protect her enough from downing. now you have another navcard, go to the navcard machine, it must have to be built in another game i would asume, use the navcard in the machine, it will shake a bit, then the a jolt of electricity will go to the top of the tower and the through the cords going into and out of the machine, now just wait a few seconds, a second bus with purple lights with a shredder on the front of it will shred all the crop in its path on the other side of the fence. Now run to the bus depot, notice that you will not pass the old bus while getting there. when you are there the bus depot lights will be purple, and a new bus will be there, i went on it, it has a packa punched b23r on the roof. if. eventually it will drive off, through the tunnel, but just before it gets too the diner it just shreds throught that things blocking the road and then it goes to another tranzit loading screen and then you start playing again! i lost connection part way through so i couldn't play it for long, it takes more than 5 hours to do, the avogrado takes so long to spawn on round 1. here is a pic from after i used the nav card and found the second bus