I'm trying to remember exactly, but it seems to me that when I walked back into our woods and found the remnants of our old All-Crop, there was a serial number tag on the left side of the unit, either on the frame that leads out to the hitch, or near where you could raise a hinged panel (again on the left side) to gain access to the straw shakers (maybe right below there). I did this a couple of months ago when we visited my brother's (he has the farm) down in Indiana. It was a small (perhaps 3-4 inches long) strip of metal with the number stamped on it. Could just still make it out though the combine has been setting back there for at least 30 years. Hope this helps. I've thought about trying to find one also. There are a few around, but not many in good shape. Good luck.