The search for a is a fool's errand. Legally, it is copyright infringement. Practically, most downloads are malware. Technically, the SCPH-90001 BIOS is the worst choice for emulation due to the problematic Deckard IOP.
The official and safest way to acquire this BIOS is to dump it from your own physical SCPH-90001 console using a tool like PS2 BIOS Dumper . Pros and Cons Ps2 Scph 90001 Bios Download
memory card to launch a BIOS dumping utility on your PS2. This will save your specific console's BIOS files to a USB drive. Alternative Legal Method The search for a is a fool's errand