I realise the problem with SD cards is that the file table on the card can easily be corrupted, especially after numerous hot-swapping (from camera to card reader, etc.). When this happens, either the entire card cannot be accessed, or the files inside are completely corrupted and thus unopenable.
You can use file recovery software to recover the contents on your card, as long as the card concerned has not been hard-formatted (ie. low-level format). Don't use consumer-grade freeware or shareware for the task, these programs may not give you the desired results.
Regarding industrial-grade data recovery software, please check your email. PM has been sent to you.