Poor Kirby looks like it spent a lot of time outdoors and got oxidized. If it's really important to get the gray bag, they do come up on eBay sometimes, but you can also ask around old Kirby dealers and mom and pop vacuum shops. The more cluttered and cramped the better, sometimes the owners are collectors themselves, or never throw anything out and they might have the part collecting cobwebs.
There's a one where I live that was built onto an old Sears Craftsman kit house and according to the owners the entire upstairs of what is the original house is his parts inventory and he throws any irreparable vacuums in the attic as well as parts that do not sell after so many years on his sales floor or get used in repairs.
Those Kirbys are tough to find original though as vacuum shops loved to butcher them with the new Kirby replacement parts of the time, which were kind of ugly colors, and then they also ripped the model tag off.
