Usually from torrent websites such as piratebay, mininova, sumo torrent, but i think you'll need a pokesave, which edits the games save file.
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well you have to download it then save it to your files
just search it up on google or try this (i dont know how far in it is) http://gbatemp.net/index.php?download=2648
you should find it at http://www.gamefaqs.com/portable/gbadvance/save/471243.html or http://www.cheatmasters.com/files/11190/Pokemon_Ruby_Files.html
You can't download save files. <--- This dude fails. you can download .sav files for nds games that is presuming you have an R4 or similar. just type in the name of the game you want a sav file for and add .sav to thend in google, it may take a bit of looking but you will find one eventualy.
For downloading games to r4card on ds, you have to download roms and have to save it into a folder. After that you have to drag and drop the files in to your micro sd.