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!.
Also, try mixing a few sounds together to create the desired sound you're aiming for. This works well for ambiences as well as sound effects.
You can also add audio to your project using the + button on the audio selection popup.
If you can’t find a particular music, ambiance, or sound effect in our extensive library, please contact us firstname.lastname@example.org to let us know what type of audio you would like to see added to our library.