Your best bet would be to check out local sex shops, if you're of age. I found them at a local, trans/gay-friendly sex shop that was just a few blocks away. They sold Underworks binders - and jacked up the price a bit, but as I didn't want anything shipped, it was worth it.
(And, funny story, when I went the first time, I was so nervous that I didn't realize the woman gave me a male binding shirt (designed for men with gynecomastia). Probably just a simple mistake, but it didn't stop me from feeling a bit flattered before exchanging it x3 )
Barring that, I know some people have luck with Walmart-bought injury binder things, and other makeshift binder things that you can get at most superstores. Might be worth checking out if the sex shop is a no-go?
