I got monster rancher on GBA emulator and DS the DS is better since it has better graphic but still the battle system is not that bad.
Let me know if you want the link
I just googled for awhile and found Roms and Emulators for the roms. I tried the ISO's but i couldn't find out how to get the emulator to read a dick for another monster. I even search for hours reading how so other people did it but it didn work for me.
The best thing i got out of searching is digimon world 1 2 and 3 for playstation