There are a lot of methods to recover deleted files from an SD card. but in your case the chances are minimum since its been over a month and you have new files in your sd card.
deleted files always goes into recycle bin (even SHIFT + DELETE but these wont be accessible easily).
your sd card does not have a recycle bin, so the deleted files goes into your comp recycle bin, and if you have deleted the files from a tablet or a mobile it will be in that devices sd card.
the new files you have copied to that device will replace the memory occupied by the deleted files there by making to impossible to recover.
http://www.filehippo.com/download_recuva/
Recuva might be able to recover your file.
EaseUS Data Recovery wizard might also help...