Peter, I’m thinking Myron Biggar was selling these kits under a Buildings Unlimited banner. The fact that you have the paperwork marked Korber. I’m guessing late 80’s early 90’s. I believe Buildings Unlimted marketed them around 1993.
If you dig through the OGR digital magazine archives you should see a number of adds around that time. I remember sending to Korber for what amounted to be a flyer showing there building. Sent a money order and waited. No internet in those days. One of my first kits was the Blackshear Refrigerated warehouse. Funny thing is. I read a little in MR on how to paint bricks and do mortar. To this day. The brickwork looks better than anything I ever did afterwards. I built it in our previous house right before we moved on the kitchen table. 34 years ago.