Forget the thunder 5- .410 is a crappy round out of a shotgun, out of a pistol it's a joke.
I've never had a black bear act aggresively enough that I felt the need to fire at one in self protection, so you could probably just carry whatever pistol you would normally carry. However if you are worried about bear trouble and are comfortable shooting a 44 get one (i.e. the biggest gun you can comfortably shoot).
I suppose you could kill a bear with a 10mm Glock, better you than me (not that I want to have to plug away at an angry bear with any handgun).
Seems like it's gotten tougher to get the hot 10mm rounds that are good for hunting. Maybe Norma still makes them? I've heard that a lot of 10 is down loaded to 40 levels, but I haven't shot much 10 lately