It's probably a Torx screw...
Use Google Images - search for "torx" to see the style
Torx drivers are available in tool stores, hardware and DIY shops.
Sadly however, my guess is that your broken Irons do not have shorted cords but blown elements. Modern irons seem to be designed and made to not be repairable - we are encouraged to buy new.
Peccavi, May 2009