The plastic analog Diana+ camera is cute, so it stands to reason any accessories would continue the cheap, jet-age theme. The "Flash for Diana+" meets the challenge, turquoise housing and all. And even if you don't own one of the retro-reissue film cameras, the Flash includes an adapter so you can use place it incongruously atop a fancy, modern DSLR.
It's $60, though — nearly as much as the Diana+. Worse, it's available (for now) only at Urban Outfitters, the hipster mall store that blithely steals from indie designers.
I think I'll stick with my current plan: smudging up a cheap lens for my DSLR and then adding some blur and saturation effects in Photoshop.