I am still searching, and I did find something like http://www.ebay.com/itm/New-PSP-2-Axis-Analog-Thumb-GAME-Joystick-Module-3V-5V-For-arduino-PSP-GM-/262136733630?hash=item3d08911fbe:g:-zsAAOSwvUlWqb0a which should theoretically work, it just might be slightly taller or shorter, and the pad might not be able to come off (if you are fine with that). All that it should take is to just desolder or cut off the horizontal header pins already soldered on, so that screwing it onto the front would go easier.
If you are worried about the metal parts on the sides that are sticking out making screwing it into the front difficult, I did also see ones like this http://www.ebay.com/itm/1PCS-New-PSP-2-Axis-Analog-Thumb-GAME-Joystick-Module-3V-5V-For-arduino-PSP-K9-/222333274071?hash=item33c41887d7:g:9CwAAOSw-0xYQUrX
This is also all assuming the board that the joysticks are soldered onto are basically the same size. It looks like they probably would be, but hard to be sure without buying them.