They used to sell those in all the cheesy tourist shops around here, as "Old Indian Weather Rock." I'm sure you could find one somewhere in Billings. Or just make one.
Last time I traveled to Britain, around 25 years ago, I took gifts for some family friends over there in Durham. They had a teenage boy with an odd sense of humor, and so I gave him an "Old Indian Weather Rock." I figured it would be good for a chuckle, but they all seemed to think it was the most uproariously funny thing they had ever seen. Every morning the boy would run outside with the rock to check the weather, then they'd all gather round to see what it said. Their reaction was way funnier than the actual joke.