You can find the Gran Turismo 4 (USA) file within the PS2 USA Redump CHD Collection hosted on the Internet Archive Download Instructions: Internet Archive Part G collection page Scroll down to the Download Options section on the right side. to view the full list of files. Gran Turismo 4 (USA).chd in the list and click it to begin the download. File Details:
.chd (Compressed Hunks of Data), which is a lossless compression format often used for PS2 emulators like PCSX2. Approximately 4.3 GB. Download Gran Turismo 4 -USA-.chd