1969 Reverse Light Switch??

Someone please help. I'm no idiot when it comes to cars but I own a 1969 Chevelle Malibu with a 350 L-48, 4-Spd. M-21 Muncie. The shifter is on the floor with no console. I am trying to locate the reverse light switch. Every parts store I go to says they can't get it or they give me the column mounted switch. This does me no good since the column never knows when the tranny goes into reverse. I just put the tranny back into the car and didn't see any locations on it that would lead me to the switch. Does anyone have any ideas? Am I just looking over the obvious? Any help would be appreciated. Thanks.