I’m located in Grand Rapids, MI and started going to B-K as a youngster. We had 4 of the traditional green & whites here in GR and a 5th was the new style rolled out just before they went totally belly up in 2002. My sister waitressed at their 28th & Eastern store all through H.S. & College in the late 60’s.
The home office/commissary was in Battle Creek, MI and they had a 2nd commissary located in Vandalia, OH.
I Googled "Bill Knapp’s Restaurant" and up came this story originally published in 2004 in the Battle Creek Enquirer.
This story has names of many people Including Jerry & Barbara Hill who in 2004 still lived in Michigan somewhere along Lake Michigan and if you are able to contact them they may be able to help you out and possibly give you the name of the ad agency that produced their commercials and the one you starred in. Hopefully you can remember the date and you obviously know the store location. My guess is the commercial was produced by a Michigan or Ohio based advertising agency.
Good luck in your quest – What a nice family Christmas gift to be able to come up with a copy put on DVD.