Macromedia Flash Player 7 for Pocket PC 2003 and Windows Mobile 5.0 devices can be downloaded from Macromedia.
TIp: If you’d like to play .swf files in Pocket Internet Explorer on the device, check this thread on XDA Dev Forum where a hacked version of Macromedia Flash 7 cab file is available for download (There seems to be a bug in the self registering section of flash.dll in the original cab file!)