There are only six cassettes in the game, all of which can be found at your work place. The locations are as follows:
Cassette One - Ground Floor, Women's Bathroom.
Cassette Two - Ground Floor, Warehouse. (All the way to the right of the Ground Floor.)
Cassette Three - First Floor, first door on right.
Cassette Four - Second Floor, second door on right,
Cassette Five - Third Floor, second door on right.
Cassette Six - Beat the Anarchy Man game.