Backup light switch, column mounted,1980 3ott

[C10wip]

My backup lights won't come on, and I have traced to it to backup light switch. This is a 3 spd, 3ott and the switch is mounted on the column by the firewall, and there is no transmission mounted switch. The circuit not including the switch is fine; if you jumper the connector the lights come on.
The switch does not seem adjustable as there are tabs which fit into the slot on the column and hold it in position. With the switch out I can feel the plates come across as I move the shifter so that seems OK. However, with the switch installed, it feels like the plates are riding up over the sliding part of the switch and not moving it ( can feel a "clunk" ). The switch is OK electrically and works if you push the slider over by hand, although it is stiff; tired lubing it a bit with silicone and that did not seem to help much. So, I figure the switch is just clapped out mechanically and I want to replace it but I can't find the part - I have looked at all of the usual suspects and only thing that looks like it is LMC part number 36-0665 - which says "is not available at this time".
Does anyone have a GM part number or knows who carries these?

Thanks.