If you need much longer consider one of the older model Sony MP3s. Look on their website and you can find a model with FM radio as well. I have one without FM that last up to 25 hours on a single USB charge.
My Venuezalan colleague says that if you are visiting Caracas then head to Sambil Mall (Largest in City). They apparently have a Nike store and various other sports stores covering Reebok, New Balance and Mizuno.