The big knife thing, don't even go there. The first step is to purchase James Gary Shelton's bear attack trilogy, if the subject interests you, you won't be able to put them down. Stephen Herrero's book is a good follow up to Shelton. Knowledge is power, and there's lots of power in these books. Now does he want a gun, or is it that you that wants him to have one? Lots of the old time woodsmen don't seem to think carrying a firearm in black bear country is important, and you won't convince them otherwise. If he wants one, continue reading, otherwise there's little point in continuing, after all, your dad has made it to 78, and old guys aren't anxious to change their ways.
If he wants an off season bear gun, the key is to finding him something appropriate, that isn't such a nuisance to carry that he'll be inclined to leave it behind, which probably leaves out a shotgun, or a big rifle. A Mares Leg in .44 magnum, fitted with a rifle sized butt stock, ghost ring and post sights, and a sling and swivels would probably give you both piece of mind, provided he's an experienced shooter. Another option, if he prefers a bolt gun, is one of the new breed of short barreled ultra light rifles in say .30/06, which allows a low power scope to be easily mounted if he has trouble finding a front sight, and there are numerous options and a broad price range in this category.
Thanks for the info. He'd probably be hard to convince to carry the gun, all my idea. He'd say it'd prevent him from carrying more baskets of berries out of the bush, and an extra 5-8 lbs over a few miles gets tiring.