No there isn't since images ripped from a CD or DVD are called ISO, images ripped from cartridges are called ROMs. Iso is an image and PSX is the name of the PS1.
Like um ISOS are names given to images or files from a CD or DVD. The name given to images or files from cartridges are called ROMs. They are named different because they are recorded on different storage devices. Correct me if I'm wrong.
That's just technical differences. Yes, there are PSP games available for download, we don't host them on RomUlation but you can find some posted in our Trade Section.
You talking about commercial? Check in the PSP Trading Section, plenty there. If you want homebrew, go to http://www.psp-news.dcemu.co.uk/