Be creative when you are using the search functionality in the Track Selection tool to find that perfect sound. It might be hard to find a polar bear roar, but a dragon roar might work perfectly. Using the effect of "Glass Cup Water" (the sound of a glass being set down on a table) as the sound effect for someone grasping the handle of an axe is another example. Even if it's not the most conventional idea, if a sound works for your story you should use it!.
If all else fails, mix a few sounds together to create the sound you're aiming for. This works well for ambiences as well as sounds.