Well, you can always buy a DS flash cart and play the ROM on a DS with full functionality and online capabilty.
That being said. I say you shouldn't do that. I've pirated games my whole life. And up until recently, I've justified it and worked around it, and in the end, I've come to the conclusion it's very close to stealing.
I know all the arguments against it, as I said, that's how I used to justify it, but like, the only difference between you downloading a ROM and you shoplifting a game is that you aren't stealing the hardware, which honestly, usually doesn't top $5.
I've stopped pirating games, and it's a load off my chest. I don't go anal on people who do, but yeah. I do still play emulators of older games of past generations.
I mean, if the company itself isn't selling them anymore, I don't feel so bad. Maybe I'm backward, but whatever.