There are many of these units available (common as NOS) since they set on dealer shelves for years I believe.
https://www.flickr.com/photos/advance-design_parts_co/14090407790/in/album-72157631868452754/
These were a divisional item, Chevy-Buick-Olds-Pontiac-Cadillac, so if you search in places like Hemmings, eBay, etc. Look for vendors or parts with a wide net. I have an earlier version but do not have directions for your version. Directions and requisite part lists may be found searching for online postings under the different GM divisions.