A lot of it boils down to trial and error and trying roms from different sites. Emu Paradise in particular has a lot that I've managed to get working just fine. Make sure you goto the Neo Geo (Arcade) section though and not the Neo Geo CD section. I would also recommend searching the torrents. Underground Gamer specifically. If using any other torrent site, try using "GP2x ROMSET" or "GNGEO ROMSET" or other variations as your search criteria. I've found several that were entire copies of someone's SD card. If you want any more specific links just hit me up in PM.