I'm guessing this is an incomplete clause that is part of a larger sentence. In this context, it looks like it means that Mark uses the knife to stab the bear repeatedly. The author says the knife finds the bear because it makes it sound like Mark is doing the action without thinking, as if the knife were acting by itself. In short, it is not a special phrase. It is just personification of the knife.

The complete form is just about the same. Mark's knife found the bear over and over again. It is fine. Here "finding" means connecting with, stabbing, whatever that sort of knife does, . With any such weapon, when fioghting, there is a chance that you will not be able to actually wound the oponent. In this case, Mark managed to wound the bear over and over again, many time. . Works for an arrow, too. He shot 4 arrows. Each found the target with precision. . They fenced till at sundown. It was only a short time till his blade found the other's heart.

It is a common usage referring to a weapon and a target. We say a weapon--such as bullet, arrow, knife, or spear--"found" its target if it hit its target accurately. I've chosen some usage examples I discovered by performing a Google search of Project Gutenberg. These are not well-known pieces of literature so I haven't bothered to give title or author. "a moment later there came another explosion as the second torpedo found its target..." "No cry came in response, but he believed that the hunter's bullet had found its target." "One gun, however, found its target, and that was one aimed and fired by the hand of Lord Desborough himself..." "The rock brushed Rick and found its target." "The two-foot swagger stick in the hand of the police officer found its target." "Edmund's axe had found its victim..." Here, it refers to unkind word rather than a physical weapon: "I saw things only from my own point of view, and was keenly sensitive to their politely concealed disapprobation, and my offended vanity found its victim in Miles."

>moved to answers