To answer the search query directly: There is no single "official link" for all PS2 BIOS files including the SCPH-90006, because such a link would be illegal. However, you now possess the knowledge to:
You may see references online to a “new SCPH-90006 BIOS link” or “final PS2 BIOS.” This does refer to a newer BIOS version (v2.30 is the last official release). Instead, it refers to: all ps2 bios files including the new scph90006 link
Different PS2 models have different BIOS versions. While most games run on any BIOS, certain titles or homebrew applications require specific revisions. Collectors and power users want "all" BIOS files to: To answer the search query directly: There is