Of course the expensive way to go if you can't find the original vendor is to basterdize a replacement wiring harness or two for the connectors and use a GM harness tool with a GM repair kit. Or try Aveco, they make some replacement connectors for GM repair work by independent shops. If you are crafty and their available, hit-up the GM parts counter guy to look up the original part number that their shop uses for the factory harness repair. Its called out in the original GM parts blueprints! The problem though is sometimes there not available yet since the cars are so new. Like I said in the beginning though, if you wrecked the car, and a body shop had to replace the harness, they would get it from somewhere! Where there's a will.......and a pocket book!
Oh, and lets not forget that some of our vendors must have made a contact or two at their manufacturers, who just happens to have built-up a nice vendor library after being in the automotive business for 30yrs or however long. They are still a great source, after all somebody's gotta go to all those darn trade shows every year and collect all those brochures!