I'm underage too and got an underworks binder just fine. What's your trouble with it?
If it's 'cause you need a credit card...very easy solution. A prepaid Visa. You can get them at most banks, I think...maybe even at Wal-Mart or somewhere like that.
Edit: In case that doesn't work out, an Ace bandage may do the trick if you're small enough. I thought it was an absolute hassle though, and I have acid reflux...something about how tight the bandages were made me really miserable. It would make my reflux flare up every single time I binded. They also have a really bad tendency to slide down, so you have to constantly re-adjust.
I'd say definitely get one from Underworks, if you can.