It looks like Emdkay has it (see the top sticky thread in this Artwork forum). He's best reached on Google Chat. Here's the relevant files from his listing:
U:\Arcade Artwork Database\O\Outrun\Outrun Full Sideart-R.psd
U:\Arcade Artwork Database\O\Outrun\Outrun Full Sideart-set print-2.psd
U:\Arcade Artwork Database\O\Outrun\Outrun Full Sideart-set print.psd
U:\Arcade Artwork Database\O\Outrun\Outrun Full Sideart.psd