Disco 2 ecu map reader/downloader

does anyone know an open source map reader/downloader that will work with a td5

It's highly unlikely that you'll be able to find anything "open source" to do with the map or remapping of the Td5 ECU. Even finding a cheap code reader will be problematic. The diesel Discovery is fitted with a suitable OBD type socket, but wasn't compatible with OBDII protocols until the release of the Disco 3 in mid-2004. Prior to the 2004 change-over the Disco used Land Rover's own protocols. The petrol Discos were compatible earlier, in about 1996.
The only code readers known to give truthful results on the diesel Disco 2 are the Nanocom, Hawkeye and Lynx for the DIY market and the Testbook T4 which is essentially the main dealer's diagnostic system.

Nanocom