Lets think about this logically: what type of situations are you going to need a backup gun in?
You are hunting with a .460 revolver which is more than potent enought to take a little black bear (and yes they are little compare to other bears). When you encounter a bear you will probably allready have your .460 out or just as close as you backup gun, so why would you need another gun?
1. Your revolver fails.
2. You miss, either with all 6 or the gun jams.
3. You hit but only wound the bear, again with all 6 or the gun jams.
In the 1. if the bear doesn't notice you, you should have time to draw your other gun and fire. In all three, if the bear notices you it will either run away or charge. If you need a backup, you will need it FAST, I would recomend an auto loader (like the 10mm). Draw quick, empty the mag, and pray.
.357s, .44s, and other revolvers are all good against bears, but don't offer you anything that your .460 doesn't. If I was hunting with your setup, my back up would be a high capacity auto so that when the SHTF I can bet my life on 12 10mm rather than 6 .44 mags.
Also the best backup is to have a buddy with a 12ga at your side (lots quicker than drawing anouther gun)