Metra has a new 28-pin harness that is much closer to what you want:
AX-SUB28SWC.
It has a yellow male RCA plug (connected to the correct pins for the OEM rear camera), and a yellow lead for the 6V camera power (
CAUTION: Ignore Metra's instructions that say to connect that wire to your car's +12V Battery/constant power!).
The harness also has leads which provide the car's reverse gear, parking brake, and speed signals (VSS). The only thing it lacks is a lead for the OEM speaker amplifier trigger.
I can put together a modified version that omits the unneeded ASWC (steering wheel) portion, and adds a blue/white wire for amp trigger. FFI, e-mail me (or if you PM me, include your e-mail).