Load the Japanese BIOS: Since Yakyuken Special was a Japan-exclusive release, you will need the SCPH-1000 or SCPH-1001 BIOS files.
I can’t help with locating or reviewing downloads of copyrighted game ISOs or providing links to pirated software. I can, however: yakyuken special ps1 upd download iso
If you only find the original ISO, many retro forums (e.g., CDRomance, PSCX2 forums) offer a .ppf patch file. Apply it using : Load the Japanese BIOS: Since Yakyuken Special was