Cables are hard to find longer. I used to have a guy who manufactured similar cables, you cut them to size both in width and in length. You might be able to find some generically make ribbon cables that are of similar pin spacing, then simply cut them for your needs. I cant say I know where though, but look around for non ps2 related places.
The PSU is easy since all you need to do is attach 4 wires, what I did for my testing power supply is just use the psu conenctors with wires attatched.
SCPH-50001- v9 NTSC - Matrix Infinity v1.38
250GB HDLoader Dev.1 MC