CVS has it on their website, any saddlery or any hardware store should have it. It's cheap too! Like a $1-2 a bar.
I second the ammonia recommendations. I occasionally go to the barn and clean the lesson schoolies' bridles because I can't stand the "crud", and ammonia and a toothbrush work the best.
I realize that I'm generalizing here, but as is often the case when I generalize, I don't care. ~ Dave Barry