I've found that it pays to use Google liberally when you have a question on this stuff. While the answers here are valuable, it sometimes takes a while to get to exactly what you need. And you might have to piece together 4 different posts until you get the combination that will fix your problem.
I Googled "3 lever switch connector" and found this. It should answer at least 2 of your unanswered questions:
Connector (28-51 Cannon Plug) For 3 Lever Light Switch, 7716895.
I can't get the picture big enough or clear enough but it looks like the comment I made about unsoldering/resoldering your old one might work. You'd need to ask the dealer if that's the way it's installed that so you'd know what was involved if you bought one. If it is a solder-on, Emmado's comment is really right-on. That's a lot of soldering. 2 would be plenty for me.
There are lots of other dealers on the 'net that probably have them but Google isn't picking them up.
By the looks of things, you'd only get the connector w/ wires w/ a take-off, and I suspect that would ruin the resale of the harness. If that's the case, I wouldn't expect to find one easily. If you do, you'd need the wire markers on it if you wanted to avoid a lot of hassle hooking it up.
Here's an NOS harness and I think I can make out the connectors. You can see that the harness is a helluva lot more valuable than the connector, even used.
Wiring harness front | M35,M35A2 | Military Vehicles For Sale | Military Trucks For Sale | M35 A2 | 5 Ton | M151 A1 A2 | Surplus Parts - TNJ Murray
I got some valuable information and suggestions from SS last week on my stop light problem but I ultimately solved it w/ a known-good 3 lever switch, Google, the TMs, and a lot of troubleshooting patience. Because I wanted to get it behind me, I ordered a turn signal switch that I really didn't need after I did some cleanup that nobody mentioned but that common sense dictated.
Just some friendly advice in trying to help you get this fixed ASAP.
Steve