One reliable source for the ISO file is the gaming community forum, GameFAQs. You can search for the game and find a verified link to the ISO file.
Bandai Namco and CyberConnect2 ended PSP development years ago. The last official Naruto game released for the PSP was Naruto Shippuden: Ultimate Ninja Impact (2011) and Naruto Shippuden: Kizuna Drive (2010). Naruto Shippuden Ultimate Ninja Storm 5 Ppsspp Iso File