After much internet research, I believe you are referring to "Why We Walk" by Phil and Julie Vassar and is also performed by the Mamasitas. It seems the only place you can purchase it is along with a book, unless it is available on ITunes or something. You can get the book and cd here: http://www.pinkribbonshop.com/index.asp?PageAction=VIEWPROD&ProdID=486

 Here are the lyrics:

There's an empty seat at the dinner table Where a mother used to sit. She was 34 years old, full of life and dreams And two small kids. There's a young man with a tear in his eye and a pink ribbon on his coat In memory of the only love he'd ever known.
There's a lady looking in the mirror without a single strand of hair. She barely recognizes the woman standing there. She's waging a silent war against an enemy inside And putting up the fight of her life.
That's why we walk. Walk to remember. We walk to celebrate. That's why we walk. Leaning on each other And holding on to faith. For those who are gone and those that live on, We honor them all. And that's why we walk.
She lays in a cold small room in a baby blue paper gown, Anticipating what the x-rays might have found. Then she hears the words that always stop you on a dime, And prays that they found it in time.
That's why we walk. Walk to remember. We walk to celebrate. That's why we walk. Leaning on each other And holding on to faith. For those who are gone and those that live on, We honor them all. And that's why we walk.
For life, for love, for one another, For him, for her, there's strength in numbers
And that's why we walk...

 Hope this helps. :)