Sell this online as a flash drive. Market on gadget sites like gdgt.com, engadget, gizmodo. Post to community sites. I don't know if ThinkGeek accepts designs but it seems like the kind of thing they would eat up.
You could start a product line of nostalgia/kitschy/personalized flash drives.
Now, slightly more seriously, I have been looking for something that could do disk emulation from image files stored on a USB drive. I have Apple IIs, Amigas and Ataris that would be more than happy to run software made for them once again.
In the case of the Ataris, the SIO bus makes it easier. In the case of the Disk II (one of the comments mentioned it), the signaling is very low-level and would, presumably, be a pain to emulate.
Don't have an Atari 400, but wish I had the circuitry know-how to pursue something like this for the Commodore disk drive.