I responded back to Weber one more time and asked if they could share any further details about the rarity (or not) of these replicas. He responded:
"...I'm afraid we don't release the production numbers of any of our products, but I'd consider this grill to be rare, although it's certainly not the only one out there. Your mother-in-law's is the first I've ever seen a photo of in all the years I've worked here."
So there are at least a few more floating around in the wild.
Holy Grails: anything 1970