This guy claims that his charger puts out 1A. It is intended for an Ipod, but it looks like if you supply your own USB to mini-USB cable it should work. The voltage is correct.
**Disclaimer: I have not tried this product. I just Googled 1A car chargers. Use at your own risk**
http://cgi.ebay.com/Capdase-iPod-USB...QQcmdZViewItem