You might try taking it in to a car stereo shop; they might be able to rig up something pretty cheap. In all honesty, you don't need the harness as long as you have some way of connecting to the pins ...

Aiwa. Remember them? They established their name manufacturing hi-fi components in the ’70s and ’80s. In the ’90s they went mainstream. Boomboxes, portable CD players, headphones, speakers, ...