Before you search for a download link, understand the law:
The Ethical Alternative: If you own the original console (e.g., a Japanese GameCube or a Namco 246 arcade board), you can extract gxrom.bin yourself using a hardware flasher like an EEPROM reader. This is legal, safe, and ensures you have a clean file.
One of the biggest issues with searching for this file is the confusion surrounding the naming convention.