well the first keller tape is in vapl-58 power station somewhere in the vault 101. the second tape is in hallowed moors cemetray north of big town. the third one is in grisly diner. the forth one is in Travel to Rockbreaker's Last Gas and turn to the west. You will see the Sniper Shack at the top of a cliff, which is the location of the fourth Keller tape. Make your way around the cliff from the left side of the mountain, where there are a super mutant and a super mutant brute. Enter the shack and the tape will be on the workbench on the left.
This is also where the Victory Rifle is located.
the last one is in a super mutant camp on anchorage place.
hope i help.