OMG.... the thread is actually back on topic 
If you are up to modifying, a Svord machete with the point rounded into a spear yet leaving the primary spine unchanged would give you a small ~11"(12" unmodified) machete that would still be useful for camp/bush tasks and which weighs less then 10 ounces. If you feel comfortable you could sharpen the backside of the point to really make it a good stabbing weapon, due to the flared blade the rest of the spine could be left alone yet remain effective for stabbing, handle can be wrapped to remove the orange and for a man it kinda needs to be, its rather smallish it does however provide a deep grip that's unlikely to allow hand to slide forwards when stabbing.
Really a question of how much room a person has when a bear is on top of them.... 11" blade could be to long or not, do you want a blade that has other uses or not?
Bayonets are made for stabbing have a guard so your hand cant slip forward and come in a range of sizes and pretty much suck for any normal knife work, yet if you feel the need to get stabby with a bear could be the best option.
Modern puukko M95 ranger knife 6" blade
Do you want a knife thats just for bears? or one that can be used for bear defense?

If you are up to modifying, a Svord machete with the point rounded into a spear yet leaving the primary spine unchanged would give you a small ~11"(12" unmodified) machete that would still be useful for camp/bush tasks and which weighs less then 10 ounces. If you feel comfortable you could sharpen the backside of the point to really make it a good stabbing weapon, due to the flared blade the rest of the spine could be left alone yet remain effective for stabbing, handle can be wrapped to remove the orange and for a man it kinda needs to be, its rather smallish it does however provide a deep grip that's unlikely to allow hand to slide forwards when stabbing.

Really a question of how much room a person has when a bear is on top of them.... 11" blade could be to long or not, do you want a blade that has other uses or not?
Bayonets are made for stabbing have a guard so your hand cant slip forward and come in a range of sizes and pretty much suck for any normal knife work, yet if you feel the need to get stabby with a bear could be the best option.
Modern puukko M95 ranger knife 6" blade

Do you want a knife thats just for bears? or one that can be used for bear defense?
I have had two near bear encounters in 3 days.
http://www.bladeforums.com/forums/showthread.php/1296066-Connecticut-black-bear-and-fleeing-women
One time all I had was a small pocket knife. The other an AMT .380 backup which was in my pack. Also there was a Enzo 12c27 knife. But what knife should I been packing to protect myself from an inevitable mauling?