This is the place you need
http://nds.cmamod.com/download.html
This has lots of progs and you need one of the ETOOLS depending on the save size on the DS cart.
I recall when I did this with my mario kart DS card, i used EToolSMS 2.1 with my EZ-flash III and selected the save size in the EZflash client menu.
Then I just followed the menu on the program when run on the DS and Bingo, it creates a save file.
This may not be that easy for you, and indeed this did take a long time on my own to figure out how to get these programs working
Best of luck
PS - when you download which ever program you get, there are some mediocar instructions, check em out
Peace