Tramp,
I'd try an electronics supply house. One in my area has a plug catalog that is 4" thick! My guess is that GM didn't make your connector but rather bought it somewhere. If it is a standard type, the electronics industry probably still sells it.
Also, you might try a junk yard for a GM car or truck a little newer than yours that may have the same connector. The little pins and receivers in the connector usually come right out by releasing a spring finger.
Les
