Once i had completed the game with only the final mission remaining i had around 487 fame.
Then i used the other members from my group who had low stats. for every level you get them up ,e.g getting to cardio level 2 etc... you get 1 fame. i chose the characters that had 1 star cardio shooting and fighting etc
then i ran around using snacks to get my cardio levels up then took out zombie hordes with headshots and cleared infestations. took around half an hour to get from 487 to 500.
i stopped using them once their stats got to level 3 or soo just to save time
I also believe finishing the last mission will get you to 500 but didnt want to risk it and had to waste time whilst i was waiting on buildings getting completed.