Well now that we have significantly slaughtered the fallen on earth. I have found that on Venus as son as you get into the city to the right of your patrol starting location you will see some buildings and cars with Fallen swarming them. If you look to your left on the road leading in you will see a rock then a car husk if you remove all the fallen then fall back to that rock you will have a clear shot at the doorway across the street where Shanks, Dregs and Vandals spawn. Happy Hunting!