A PlayStation 2 (PS2) BIOS is the mandatory system software required by emulators like PCSX2 to boot games. Because this firmware is copyrighted by Sony, it is generally illegal to distribute or download from third-party sites; the legal method is to "dump" the BIOS from a console you physically own.
To stay within legal boundaries, you must extract the BIOS from your own hardware. Search Results for ps 2 bios
: A newer technique allows for extracting BIOS files from official PS3 firmware updates available on Sony's website using specific batch tools. Extract Your Own PS2 & PS1 BIOS (No Console Required!) A PlayStation 2 (PS2) BIOS is the mandatory
PS2Ident or the PCSX2 BIOS Dumper to extract the ROM chips to a USB drive. Search Results for ps 2 bios