I went about this quest the wrong way. First i found the cellar with the rogue NCR soldiers that wanted to raid the police and fire station. After that i got the mission to kill feral NCR soldiers for tags. Now there are no feral NCR soldiers left to kill (need 10 tags to finish the quest). Can i get these at some other location in the game?

Camp Searchlight is good for that.

Nine out of ten are found outside from the ghouls. The tenth is on Private Edwards, who can be found in a house close to the west side church.

I had this problem too. I entered Camp Searchlight from the east so I killed all the ghouls and discovered the NCR soldiers after that. The bodies of the NCR ghouls appear to have remained in my game so if it's the same for you then you can go find them. I had to add them using the console in the end

How do i get the last ones using a console?