CrossRoads:
Allegro makes the UDN2891A-T that will source 500mA.
http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?freeText=udn2981&langId=-1&storeId=10001&productId=1762681&search_type=jamecoall&catalogId=10001&ddkey=http:ParametricXmlView
.. but you'd better not drive more than one channel at a time, because the saturation voltage drop will enough to probably overheat the package even if you drive just two channels @ 500mA.