I didn't want to buy one, since I knew I could just make one myself.
I simply used a car mount from an old Nokia N810 Tablet PC I once had.
And the end result is quite awesome!
In this image you can see I was playing an old Legend of Zelda DX
for Gameboy color. (My favorite from the old classics.)
Headphones and USB cable are also easily accessible
by simply removing the bottom padding and replacing it with a smaller one.
Playing all games on the GO are now more comfortable then on any previous model PSP.
Even the Controllers USB port is accessible.
Tell me if you like.