The 'special solar sauce' in the solar charger is detailed in the design notes:
http://learn.adafruit.com/usb-dc-and-so ... sign-notes
A standard charger such as #280 can work, as long as you have strong and steady sunlight and a big enough panel to keep the voltage from collapsing under the load. My personal experience with this charger and a 3W panel as a power source on a mountain trek was that is was not reliable enough to justify the pack weight.
If you
sign up for notifications, you will get email as soon as the solar chargers are back in stock.