You could try R- Studio.
Data Recovery Demo and File Recovery trial software download I haven't used it but with luck your SD card is/was FAT formatted and the demo version will recover files up to 64KB which would recover quite a large B4ppc source file. If it does work and you need to recover larger files then R-Studio FAT is only $50 which you may think is worth it. There are others around - Google for "data recovery" or "file recovery". In future remember to backup regularly!