Be authentic as a speaker does not mean you always have to tell stories from your life or from the lives of people you know. You can branch out and use stories outside of your inner sphere to support your points. A few reasons why:
1. Unless you are a narcotics cop in Detroit, a professional hitch hiker or Roger Rabbit, your life probably isn't full of the most interesting stories out there. Of course, most of the interestingness of a story is in the telling, not in the tale itself, but the lion's share of the stories out there at your disposal don't reside in your particular life line.
2. A big part of being a great speaker is being a great story teller, but that doesn't mean the stories have to be true to your life. True, yes. True to your life, not always.
3. As long as you get permission to use a story that is a creative piece from another speaker or author and you don't tell a story like it happened to you if it didn't, you can use as much great material as you can get your hands on.
4. Sure, there are a large number of speakers out there who have great life stories. Either very tragic, heroic, hilarious, etc. And there are those presenters who have the Seinfeld Gift - they can take the simplest, most ordinary story and make it into something worth listening to. However, just because you haven't lost your leg or haven't made it to the Olympics or you don't have the gift of being able to make cotton balls hilarious, doesn't mean you have to use something other than great, epic stories to support your message.
Will all this great support for searching out great stories from sources other than your life, it is important to add the cautionary tale that you do probably have more interesting stories from your own life worth telling than you think you do. So, I do suggest you search through your personal library of coolness before you expend too much energy in the rest of the world's book store. Good luck and tell 'em like you mean it...