I've been hunting down obscure PSP stuff for years, so this one hits home: legally downloading 'Dead Head Fred' depends mostly on whether Sony or the rights holder ever put it up for sale digitally. First place I’d check is the
PlayStation Store (the official PSN storefront) — search there from a PS3/PSP/PS Vita or the web store. If it's available as a digital PSP title you can buy it there and download it legitimately to a compatible device.
If you don’t find it on PSN, the next honest route is buying a physical UMD. I buy a lot of older PSP UMDs from places like eBay, Discogs, local retro shops, or trusted sellers on Amazon. Owning the UMD gives you a lawful copy to play on original hardware. Check the seller’s condition notes and photos; UMDs can be beat up, and sometimes people include the manual scans which I love for nostalgia.
Finally, if neither option exists, it may simply not be available for legal download. You can try contacting the publisher or dev via email/socials to ask about re-releases, or keep an eye on remaster news. Also remember: in some countries you can legally make a personal backup of media you own, but laws vary — so look up your local rules before doing anything technical. Personally, I prefer hunting down the UMD and playing it on real hardware whenever possible.