Joan, I've done some looking but haven't had any luck with your problem. I've tried several different kinds of searches and haven't come up with anything.
In 1840 it looks like Reuben Yates was in Conway Co, AR. The early marriages there before 1850 were apparently destroyed so if that's where John and Talitha were married there is no record. The same goes for Marion Co, AR. That courthouse burned and destroyed almost everything before 1880.
I've tried looking for counties in both Missouri and Arkansas with both Graves and Yates families in 1830 and 1840 but that didn't turn up anything that looked promising.
Is it possible that Graves isn't the correct maiden name for Talitha? Where does that information come from?
As for bear hunting, it was pretty common in southwest MO and northwest AR. The Turnbo manuscripts, tales of life in the Ozarks, are full of bear hunting stories. I don't know if this will work, but it's a link to bear hunting tales from those manuscripts.